题目地址：http://poj.org/problem?id=2752

题目：

每组数据给定一个字符串，从小到大输出既是前缀又是后缀的子串的长度

ac代码：

直接用hash做，比kmp简单很多

#include <cmath>
#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>
#include <vector>
#include <algorithm>
#include <stack>
#include <queue>
using namespace std;
typedef unsigned long long ll;
const ll maxn = 400005;
ll p = 233333,len = 0;
char s[maxn];
ll has[maxn], power[maxn];
void init()//预处理p^n
{
    power[0] = 1;
    for(int  i = 1; i < maxn; i++)
        power[i] = power[i - 1] * p;
}
int main ()
{
    //freopen("/Users/zhangkanqi/Desktop/11.txt","r",stdin);
    init();
    while(~scanf("%s",s+1))
    {
        len = strlen(s + 1);
        has[0] = 0;
        for(int i = 1; i <= len; i++)
            has[i] = has[i - 1] * p + (ll)(s[i] - 'a' + 1);
        for(int i = 1; i <= len ; i++)
        {
            ll tmp = has[len] - has[len - i] * power[i];
            if(tmp == has[i])
                printf("%d ", i);
        }
        printf("\n");
    }
    return 0;
}