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增加目录
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@ -1,3 +1,20 @@
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<!-- MarkdownTOC -->
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- [说明](#说明)
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- [1. KMP 算法](#1-kmp-算法)
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- [2. 替换空格](#2-替换空格)
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- [3. 最长公共前缀](#3-最长公共前缀)
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- [4. 回文串](#4-回文串)
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- [4.1. 最长回文串](#41-最长回文串)
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- [4.2. 验证回文串](#42-验证回文串)
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- [4.3. 最长回文子串](#43-最长回文子串)
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- [4.4. 最长回文子序列](#44-最长回文子序列)
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- [5. 括号匹配深度](#5-括号匹配深度)
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- [6. 把字符串转换成整数](#6-把字符串转换成整数)
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<!-- /MarkdownTOC -->
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## 说明
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- 本文作者：wwwxmu
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@ -36,34 +53,34 @@
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//https://www.weiweiblog.cn/replacespace/
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public class Solution {
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/**
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* 第一种方法：常规方法。利用String.charAt(i)以及String.valueOf(char).equals(" "
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* )遍历字符串并判断元素是否为空格。是则替换为"%20",否则不替换
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*/
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public static String replaceSpace(StringBuffer str) {
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/**
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* 第一种方法：常规方法。利用String.charAt(i)以及String.valueOf(char).equals(" "
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* )遍历字符串并判断元素是否为空格。是则替换为"%20",否则不替换
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*/
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public static String replaceSpace(StringBuffer str) {
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int length = str.length();
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// System.out.println("length=" + length);
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StringBuffer result = new StringBuffer();
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for (int i = 0; i < length; i++) {
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char b = str.charAt(i);
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if (String.valueOf(b).equals(" ")) {
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result.append("%20");
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} else {
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result.append(b);
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}
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}
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return result.toString();
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int length = str.length();
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// System.out.println("length=" + length);
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StringBuffer result = new StringBuffer();
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for (int i = 0; i < length; i++) {
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char b = str.charAt(i);
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if (String.valueOf(b).equals(" ")) {
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result.append("%20");
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} else {
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result.append(b);
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}
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}
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return result.toString();
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}
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}
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/**
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* 第二种方法：利用API替换掉所用空格，一行代码解决问题
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*/
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public static String replaceSpace2(StringBuffer str) {
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/**
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* 第二种方法：利用API替换掉所用空格，一行代码解决问题
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*/
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public static String replaceSpace2(StringBuffer str) {
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return str.toString().replaceAll("\\s", "%20");
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}
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return str.toString().replaceAll("\\s", "%20");
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}
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}
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```
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@ -93,36 +110,36 @@ public class Solution {
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```java
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//https://leetcode-cn.com/problems/longest-common-prefix/description/
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public class Main {
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public static String replaceSpace(String[] strs) {
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public static String replaceSpace(String[] strs) {
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// 数组长度
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int len = strs.length;
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// 用于保存结果
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StringBuffer res = new StringBuffer();
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// 注意：=是赋值，==是判断
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if (strs == null || strs.length == 0) {
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return "";
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}
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// 给字符串数组的元素按照升序排序(包含数字的话，数字会排在前面)
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Arrays.sort(strs);
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int m = strs[0].length();
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int n = strs[len - 1].length();
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int num = Math.min(m, n);
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for (int i = 0; i < num; i++) {
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if (strs[0].charAt(i) == strs[len - 1].charAt(i)) {
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res.append(strs[0].charAt(i));
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} else
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break;
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// 数组长度
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int len = strs.length;
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// 用于保存结果
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StringBuffer res = new StringBuffer();
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// 注意：=是赋值，==是判断
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if (strs == null || strs.length == 0) {
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return "";
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}
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// 给字符串数组的元素按照升序排序(包含数字的话，数字会排在前面)
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Arrays.sort(strs);
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int m = strs[0].length();
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int n = strs[len - 1].length();
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int num = Math.min(m, n);
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for (int i = 0; i < num; i++) {
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if (strs[0].charAt(i) == strs[len - 1].charAt(i)) {
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res.append(strs[0].charAt(i));
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} else
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break;
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}
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return res.toString();
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}
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return res.toString();
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}
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}
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//测试
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public static void main(String[] args) {
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String[] strs = { "customer", "car", "cat" };
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System.out.println(Main.replaceSpace(strs));//c
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}
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public static void main(String[] args) {
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String[] strs = { "customer", "car", "cat" };
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System.out.println(Main.replaceSpace(strs));//c
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}
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}
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```
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```java
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//https://leetcode-cn.com/problems/longest-palindrome/description/
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class Solution {
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public int longestPalindrome(String s) {
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if (s.length() == 0)
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return 0;
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// 用于存放字符
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HashSet<Character> hashset = new HashSet<Character>();
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char[] chars = s.toCharArray();
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int count = 0;
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for (int i = 0; i < chars.length; i++) {
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if (!hashset.contains(chars[i])) {// 如果hashset没有该字符就保存进去
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hashset.add(chars[i]);
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} else {// 如果有,就让count++（说明找到了一个成对的字符），然后把该字符移除
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hashset.remove(chars[i]);
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count++;
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}
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}
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return hashset.isEmpty() ? count * 2 : count * 2 + 1;
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}
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public int longestPalindrome(String s) {
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if (s.length() == 0)
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return 0;
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// 用于存放字符
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HashSet<Character> hashset = new HashSet<Character>();
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char[] chars = s.toCharArray();
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int count = 0;
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for (int i = 0; i < chars.length; i++) {
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if (!hashset.contains(chars[i])) {// 如果hashset没有该字符就保存进去
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hashset.add(chars[i]);
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} else {// 如果有,就让count++（说明找到了一个成对的字符），然后把该字符移除
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hashset.remove(chars[i]);
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count++;
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}
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}
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return hashset.isEmpty() ? count * 2 : count * 2 + 1;
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}
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}
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```
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```java
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//https://leetcode-cn.com/problems/valid-palindrome/description/
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class Solution {
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public boolean isPalindrome(String s) {
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if (s.length() == 0)
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return true;
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int l = 0, r = s.length() - 1;
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while (l < r) {
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// 从头和尾开始向中间遍历
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if (!Character.isLetterOrDigit(s.charAt(l))) {// 字符不是字母和数字的情况
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l++;
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} else if (!Character.isLetterOrDigit(s.charAt(r))) {// 字符不是字母和数字的情况
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r--;
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} else {
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// 判断二者是否相等
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if (Character.toLowerCase(s.charAt(l)) != Character.toLowerCase(s.charAt(r)))
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return false;
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l++;
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r--;
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}
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}
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return true;
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}
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public boolean isPalindrome(String s) {
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if (s.length() == 0)
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return true;
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int l = 0, r = s.length() - 1;
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while (l < r) {
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// 从头和尾开始向中间遍历
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if (!Character.isLetterOrDigit(s.charAt(l))) {// 字符不是字母和数字的情况
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l++;
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} else if (!Character.isLetterOrDigit(s.charAt(r))) {// 字符不是字母和数字的情况
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r--;
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} else {
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// 判断二者是否相等
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if (Character.toLowerCase(s.charAt(l)) != Character.toLowerCase(s.charAt(r)))
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return false;
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l++;
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r--;
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}
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}
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return true;
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}
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}
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```
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```java
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//https://leetcode-cn.com/problems/longest-palindromic-substring/description/
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class Solution {
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private int index, len;
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private int index, len;
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public String longestPalindrome(String s) {
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if (s.length() < 2)
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return s;
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for (int i = 0; i < s.length() - 1; i++) {
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PalindromeHelper(s, i, i);
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PalindromeHelper(s, i, i + 1);
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}
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return s.substring(index, index + len);
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}
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public String longestPalindrome(String s) {
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if (s.length() < 2)
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return s;
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for (int i = 0; i < s.length() - 1; i++) {
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PalindromeHelper(s, i, i);
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PalindromeHelper(s, i, i + 1);
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}
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return s.substring(index, index + len);
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}
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public void PalindromeHelper(String s, int l, int r) {
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while (l >= 0 && r < s.length() && s.charAt(l) == s.charAt(r)) {
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l--;
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r++;
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}
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if (len < r - l - 1) {
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index = l + 1;
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len = r - l - 1;
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}
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}
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public void PalindromeHelper(String s, int l, int r) {
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while (l >= 0 && r < s.length() && s.charAt(l) == s.charAt(r)) {
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l--;
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r++;
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}
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if (len < r - l - 1) {
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index = l + 1;
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len = r - l - 1;
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}
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}
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}
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```
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@ -381,20 +398,20 @@ import java.util.Scanner;
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* @Description: TODO 求给定合法括号序列的深度
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*/
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public class Main {
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public static void main(String[] args) {
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Scanner sc = new Scanner(System.in);
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String s = sc.nextLine();
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int cnt = 0, max = 0, i;
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for (i = 0; i < s.length(); ++i) {
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if (s.charAt(i) == '(')
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cnt++;
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else
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cnt--;
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max = Math.max(max, cnt);
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}
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sc.close();
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System.out.println(max);
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}
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public static void main(String[] args) {
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Scanner sc = new Scanner(System.in);
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String s = sc.nextLine();
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int cnt = 0, max = 0, i;
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for (i = 0; i < s.length(); ++i) {
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if (s.charAt(i) == '(')
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cnt++;
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else
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cnt--;
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max = Math.max(max, cnt);
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}
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sc.close();
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System.out.println(max);
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}
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}
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```
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@ -407,38 +424,38 @@ public class Main {
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//https://www.weiweiblog.cn/strtoint/
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public class Main {
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public static int StrToInt(String str) {
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if (str.length() == 0)
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return 0;
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char[] chars = str.toCharArray();
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// 判断是否存在符号位
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int flag = 0;
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if (chars[0] == '+')
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flag = 1;
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else if (chars[0] == '-')
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flag = 2;
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int start = flag > 0 ? 1 : 0;
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int res = 0;// 保存结果
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for (int i = start; i < chars.length; i++) {
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if (Character.isDigit(chars[i])) {// 调用Character.isDigit(char)方法判断是否是数字，是返回True，否则False
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int temp = chars[i] - '0';
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res = res * 10 + temp;
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} else {
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return 0;
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}
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}
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return flag == 1 ? res : -res;
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public static int StrToInt(String str) {
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if (str.length() == 0)
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return 0;
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char[] chars = str.toCharArray();
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// 判断是否存在符号位
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int flag = 0;
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if (chars[0] == '+')
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flag = 1;
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else if (chars[0] == '-')
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flag = 2;
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int start = flag > 0 ? 1 : 0;
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int res = 0;// 保存结果
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for (int i = start; i < chars.length; i++) {
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if (Character.isDigit(chars[i])) {// 调用Character.isDigit(char)方法判断是否是数字，是返回True，否则False
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int temp = chars[i] - '0';
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res = res * 10 + temp;
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} else {
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return 0;
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}
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}
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return flag == 1 ? res : -res;
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}
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}
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public static void main(String[] args) {
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// TODO Auto-generated method stub
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String s = "-12312312";
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System.out.println("使用库函数转换：" + Integer.valueOf(s));
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int res = Main.StrToInt(s);
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System.out.println("使用自己写的方法转换：" + res);
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public static void main(String[] args) {
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// TODO Auto-generated method stub
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String s = "-12312312";
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System.out.println("使用库函数转换：" + Integer.valueOf(s));
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int res = Main.StrToInt(s);
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System.out.println("使用自己写的方法转换：" + res);
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}
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}
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}
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