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
class Solution {
public boolean isPalindrome(String s) {
StringBuffer sgood = new StringBuffer();
int length = s.length();
for (int i = 0; i < length; i++) {
char ch = s.charAt(i);
if (Character.isLetterOrDigit(ch)) {
sgood.append(Character.toLowerCase(ch));
}
}
StringBuffer sgood_rev = new StringBuffer(sgood).reverse();
return sgood.toString().equals(sgood_rev.toString());
}
// 作者：LeetCode-Solution
// 链接：https://leetcode-cn.com/problems/valid-palindrome/solution/yan-zheng-hui-wen-chuan-by-leetcode-solution/
}class Solution {
public boolean isPalindrome(String s) {
StringBuffer sgood = new StringBuffer();
int length = s.length();
for (int i = 0; i < length; i++) {
char ch = s.charAt(i);
if (Character.isLetterOrDigit(ch)) {
sgood.append(Character.toLowerCase(ch));
}
}
int n = sgood.length();
int left = 0, right = n - 1;
while (left < right) {
if (Character.toLowerCase(sgood.charAt(left)) != Character.toLowerCase(sgood.charAt(right))) {
return false;
}
++left;
--right;
}
return true;
}
// 作者：LeetCode-Solution
// 链接：https://leetcode-cn.com/problems/valid-palindrome/solution/yan-zheng-hui-wen-chuan-by-leetcode-solution/
}class Solution {
public boolean isPalindrome(String s) {
int n = s.length();
int left = 0, right = n - 1;
while (left < right) {
while (left < right &&
!Character.isLetterOrDigit(s.charAt(left))) {
++left;
}
while (left < right &&
!Character.isLetterOrDigit(s.charAt(right))) {
--right;
}
if (left < right) {
if (Character.toLowerCase(s.charAt(left)) != Character.toLowerCase(s.charAt(right))) {
return false;
}
++left;
--right;
} //这个left < right去掉貌似可以，while里三处必须有.
}
return true;
}
// 作者：LeetCode-Solution
// 链接：https://leetcode-cn.com/problems/valid-palindrome/solution/yan-zheng-hui-wen-chuan-by-leetcode-solution/
}
