categories: [Blog,Algorithm]

125. 验证回文串

难度简单
给定一个字符串，验证它是否是回文串，只考虑字母和数字字符，可以忽略字母的大小写。
说明：本题中，我们将空字符串定义为有效的回文串。
示例 1:
输入: “A man, a plan, a canal: Panama”
输出: true

示例 2:
输入: “race a car”
输出: false

  1. class Solution {
  2.     public boolean isPalindrome(String s) {
  3.         StringBuffer sgood = new StringBuffer();
  4.         int length = s.length();
  5.         for (int i = 0; i < length; i++) {
  6.             char ch = s.charAt(i);
  7.             if (Character.isLetterOrDigit(ch)) {
  8.                 sgood.append(Character.toLowerCase(ch));
  9.             }
  10.         }
  11.         StringBuffer sgood_rev = new StringBuffer(sgood).reverse();
  12.         return sgood.toString().equals(sgood_rev.toString());
  13.     }
  15. // 作者：LeetCode-Solution
  16. // 链接：https://leetcode-cn.com/problems/valid-palindrome/solution/yan-zheng-hui-wen-chuan-by-leetcode-solution/
  17. }
  1. class Solution {
  2.     public boolean isPalindrome(String s) {
  3.         StringBuffer sgood = new StringBuffer();
  4.         int length = s.length();
  5.         for (int i = 0; i < length; i++) {
  6.             char ch = s.charAt(i);
  7.             if (Character.isLetterOrDigit(ch)) {
  8.                 sgood.append(Character.toLowerCase(ch));
  9.             }
  10.         }
  11.         int n = sgood.length();
  12.         int left = 0, right = n - 1;
  13.         while (left < right) {
  14.             if (Character.toLowerCase(sgood.charAt(left)) != Character.toLowerCase(sgood.charAt(right))) {
  15.                 return false;
  16.             }
  17.             ++left;
  18.             --right;
  19.         }
  20.         return true;
  21.     }
  23. // 作者：LeetCode-Solution
  24. // 链接：https://leetcode-cn.com/problems/valid-palindrome/solution/yan-zheng-hui-wen-chuan-by-leetcode-solution/
  25. }
  1. class Solution {
  2.     public boolean isPalindrome(String s) {
  3.         int n = s.length();
  4.         int left = 0, right = n - 1;
  5.         while (left < right) {
  6.             while (left < right && 
  7.             !Character.isLetterOrDigit(s.charAt(left))) {
  8.                 ++left;
  9.             }
  10.             while (left < right && 
  11.             !Character.isLetterOrDigit(s.charAt(right))) {
  12.                 --right;
  13.             }
  14.             if (left < right) {
  15.                 if (Character.toLowerCase(s.charAt(left)) != Character.toLowerCase(s.charAt(right))) {
  16.                     return false;
  17.                 }
  18.                 ++left;
  19.                 --right;
  20.             } //这个left < right去掉貌似可以，while里三处必须有.
  21.         }
  22.         return true;
  23.     }
  24. // 作者：LeetCode-Solution
  25. // 链接：https://leetcode-cn.com/problems/valid-palindrome/solution/yan-zheng-hui-wen-chuan-by-leetcode-solution/
  26. }