【初级算法】16. 验证回文字符串

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:
    bool isPalindrome(string s) {
        int len = s.size();
        int start = 0;
        int end = len-1;
        
        while(start < end){
            char first,second;
            /*get the fisrt char*/
            while(start <= end){
                if((s[start] >= ‘a‘ && s[start] <= ‘z‘)||
                   (s[start] >= ‘A‘ && s[start] <= ‘Z‘)||
                   (s[start] >= ‘0‘ && s[start] <= ‘9‘)){
                    first = s[start];
                    if(s[start] >= ‘A‘ && s[start] <= ‘Z‘){
                        first = first-‘A‘+‘a‘;
                    }
                    break;
                }else{
                    start++;
                }
            }
            
            /*get the second char*/
            while(start <= end){
                if((s[end] >= ‘a‘ && s[end] <= ‘z‘)||
                   (s[end] >= ‘A‘ && s[end] <= ‘Z‘)||
                   (s[end] >= ‘0‘ && s[end] <= ‘9‘)){
                    second = s[end];
                    if(second <= ‘Z‘&&second>=‘A‘){
                        second = second-‘A‘+‘a‘;
                    }
                    break;
                }else{
                    end--;
                }
            }
            
            if(start > end){
                break;
            }
            
            if(first == second){
                start++;
                end--;
            }else{
                return false;
            }
        }
        
        return true;
    }
};