最长回文

题目传送：HDU - 3068 - 最长回文

AC代码：

#include <map>
#include <set>
#include <list>
#include <cmath>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <cctype>
#include <cstdio>
#include <string>
#include <vector>
#include <complex>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <sstream>
#include <utility>
#include <iostream>
#include <algorithm>
#include <functional>
#define LL long long
#define INF 0x7fffffff
using namespace std;

char s[250000];
char str[250000];
int p[250000];
int len_s;
int len_str;

void get_str() {
    str[0] = ‘$‘;
    str[1] = ‘#‘;
    for(int i = 1; i <= len_s; i ++) {
        str[i * 2] = s[i];
        str[i * 2 + 1] = ‘#‘;
    }
    str[len_s * 2 + 2] = ‘\0‘;
    len_str = len_s * 2 + 1;
}

void solve() {
    int id;
    int mx = 0;
    for(int i = 1; i <= len_str; i ++) {
        if(mx > i) {
            p[i] = min(p[id * 2 - i], mx - i);
        }
        else p[i] = 1;
        while(str[i + p[i]] == str[i - p[i]]) p[i] ++;
        if(p[i] + i > mx) {
            mx = p[i] + i;
            id = i;
        }
    }
}

int main() {
    while(scanf("%s", s + 1) != EOF) {
        len_s = strlen(s + 1);
        get_str();
        solve();

        int ans = 0;
        for(int i = 1; i <= len_str; i ++) {
            ans = ans > p[i] ? ans : p[i];
        }
        printf("%d\n", ans - 1);
    }
    return 0;
}