【LeetCode】125. Valid Palindrome

问题描述

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

For example,
"A man, a plan, a canal: Panama" is a palindrome.
"race a car" is not a palindrome.

Note:
Have you consider that the string might be empty? This is a good question to ask during an interview.

For the purpose of this problem, we define empty string as valid palindrome.

回文字符串判断，但只判断字母和数字是否形成回文字符串，标点符号被略过。

问题分析

保留左右两个指针，每一轮先移动左指针获取一个字母或数字，其它字符都跳过；然后移动右指针，找到一个字母或数字，其它字符都跳过；如果此时左右两个字符都为字母或数字并但是两个不相等，则返回false；进行下轮指针移动直到两个指针相等。

代码

class Solution {
public:
    bool isPalindrome(string s) {
    	if(s.length()==0||s.length()==1) return true;
        int left=0, right=s.length()-1;
        // 大写转小写
		for(int i=0;i<s.length();i++) {
			char ch = s[i];
			if(ch>='A'&&ch<='Z') ch = 'a' + ch - 'A';
			s[i] = ch;
		}
		while(left<right) {
			char l = s[left++];
			char r = s[right--];
 			while(!((l>='a'&&l<='z')||(l>='0'&&l<='9'))&&left<s.length()) {
	        	l = s[left++];
	        }
	        while(!((r>='a'&&r<='z')||(r>='0'&&r<='9'))&&right>0) {
	        	r = s[right--];
	        }
	        if(((l>='a'&&l<='z')||(l>='0'&&l<='9'))&&((r>='a'&&r<='z')||(r>='0'&&r<='9'))&&r!=l) {
        		return false;
        	}
        }
        return true;
    }
};