[leetcode]Longest Palindromic Substring

题目链接：https://leetcode.com/problems/longest-palindromic-substring/

输出最长的回文串

class Solution {
public:
    int pre[22222];
    char x[22222];
    char str[22222];

    int min(int x, int y) {
        return x < y ? x : y;
    }

    int init(char *str, char *x) {
        int len = strlen(x);
        str[0] = '$';
        for (int i = 0; i <= len; i++) {
            str[2 * i + 1] = '#';
            str[2 * i + 2] = x[i];
        }
        len = 2 * len + 2;
        str[len] = 0;
        return len;
    }
    void manacher(int *pre, char *str, int len) {
        int id = 0;
        int mx = 0;
        for (int i = 1; i < len; i++) {
            pre[i] = mx > i ? min(pre[2 * id - i], mx - i) : 1;
            while (str[i + pre[i]] == str[i - pre[i]])   pre[i]++;
            if (pre[i] + i > mx) {
                id = i;
                mx = pre[id] + id;
            }
        }
    }
    string longestPalindrome(string s) {
        memset(pre, 0, sizeof(pre));
        memset(str, 0, sizeof(str));
        int len = init(str, const_cast<char*>(s.data()));
        manacher(pre, str, len);
        int fuck = 1, pos = 0;
        for (int i = 0; i < len; i++) {
            if (fuck < pre[i]) {
                fuck = pre[i];
                pos = i;
            }
        }
        pos--;
        fuck--;
        string ans;
        for (int i = pos - fuck + 1; i <= pos + fuck + 1; i++) {
            if (i % 2 == 0) {
                ans.push_back(str[i]);
            }
        }
        return ans;
    }
};