ACM题目————最长回文串

#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdio>
#include <cctype>
#include <cstdlib>
#include <stack>
#include <cmath>
#include <string>
#include <queue>
#define INF 10000001

using namespace std;
const int maxn = 110005*2;
char str[maxn];
int p[maxn];

void manacher(char *s, int len){
    p[0] = 1 ;
    int Max = 0, d= 0 ;
    for(int i=1; i<len; i++){
        p[i] = Max > i ? min(p[d*2-i],Max-i):1 ;
        while( s[i+p[i]] == s[i-p[i]]) p[i] ++ ;
        if( i + p[i] > d + p[d] ){
            d = i ;
            Max = i + p[i] ;
        }
    }
}

int main(){
    while( ~ scanf("%s",str) ){
        int len = strlen(str);
        for(int i=len; i>=0; i--){
            str[(i<<1)+1] = '#' ;
            str[(i<<1)+2] = str[i] ;
        }
        str[0] = '*' ;
        len = len * 2 + 2 ;
        manacher(str,len);
        int ans = 0 ;
        for(int i=0; i<len; i++){
            ans = max(p[i]-1,ans);
        }
        printf("%d\n",ans);
    }
    return 0;
}