5.最长回文子串

题目

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思路
1.字符串中的一个字符(连续相同的字符作1个字符)
2.依次对比字符两侧字符是否相等
代码

char* longestPalindrome(char* s) {
    
    int max = 1;
    int left, right;
    int maxLeft = 0;
    int totalLen = strlen(s);
    int i;
    char *res = (char *) calloc(1, 1001);
    
    if(totalLen == 1) {
        res[0] = s[0];
        return res;
    }
    
    for(i = 0; i < totalLen - 1;) {
        
        if(totalLen-i<=max/2)//剩余长度小于当前最大长度，则没有查找下一个的必要
            break;
        //first, pass consecutive numbers equal to each other
        right = i;
        left = i;
        while((right < totalLen - 1) && (s[right] == s[right + 1])) {
            right ++;
        }
        
        //second, set i = r + 1, for there is no len larger when start from i to r
        i = right + 1;
        
        //third, count those s[right] == s[left]
        while((left > 0) && (right < totalLen - 1) && (s[left - 1] == s[right + 1])) {
            right++;
            left--;
        }
        
        if(right - left + 1 > max) {
            maxLeft = left;
            max = right - left + 1;
        }
    }
    
    strncpy(res, s + maxLeft, max);
    return res;
}