【Leetcode】125. Valid Palindrome（字符串模拟）

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

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

Example 1:

Input: "A man, a plan, a canal: Panama"
Output: true

Example 2:

Input: "race a car"
Output: false

解题思路：

排除空格和标点，字符串为对称字符串。

C 库函数 int tolower(int c) 把给定的字母转换为小写字母（若为数字则保持不变）。

C 库函数 void isalnum(int c) 检查所传的字符是否是字母和数字。

class Solution {
public:
    bool isPalindrome(string s) {
        int start = 0, end = s.length() -1;
        while(start<end){
            char cs = tolower(s[start]), ce = tolower(s[end]);
            if(!isalnum(cs)){
                start++;
                continue;
            }
            if(!isalnum(ce)){
                end--;
                continue;
            }
            if(cs!=ce) return false;
            start++;
            end--;
        }
        return true;
    }
};