POJ 3974 Palindrome（最长回文子串）

题目链接：http://poj.org/problem?id=3974

题意：求一给定字符串最长回文子串的长度

思路：直接套模板manacher算法

code：

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int MAXN = 1000010;
char Ma[2*MAXN];
int Mp[2*MAXN];

void Manacher(char s[], int len)
{
    int l = 0;
    Ma[l++] = 'S';
    Ma[l++] = '#';
    for (int i = 0; i < len; ++i)
    {
        Ma[l++] = s[i];
        Ma[l++] = '#';
    }
    Ma[l] = 0;
    int mx = 0;
    int id = 0;
    for (int i = 0; i < l; ++i)
    {
        Mp[i] = mx > i ? min(Mp[2*id-i], mx-i) : 1;
        while (Ma[i+Mp[i]] == Ma[i-Mp[i]]) ++Mp[i];
        if (i + Mp[i] > mx)
        {
            mx = i +Mp[i];
            id = i;
        }
    }
}

char s[MAXN];

int main()
{
    int cnt = 0;
    while (scanf("%s", s) != EOF)
    {
        if (strcmp(s, "END") == 0) break;
        int len = strlen(s);
        Manacher(s, len);
        int ans = 0;
        len = 2 * len + 2;
        for (int i = 0; i < len; ++i) ans = max(ans, Mp[i] - 1);
        printf("Case %d: %d
",++cnt, ans);
    }
    return 0;
}