字符串哈希

不能把数字映射成0，因为一个A是0，两个A也是0，会冲突。

#include<iostream>
#include<cstring>
typedef unsigned long long ULL;
const int N = 1e5 + 10, P = 131;
ULL p[N], h[N];
int n, m;
char str[N];

ULL get(int l, int r)
{
    return h[r] - h[l - 1] * p[r - l + 1];
}

int main()
{
    scanf("%d%d%s",&n, &m, str + 1);
    p[0] = 1;
    for(int i = 1; i <= n; i ++)
    {
        p[i] = p[i - 1] * P;
        h[i] = h[i - 1] * P + str[i]; //预处理哈希值
    }
    while(m --)
    {
        int l1, r1, l2, r2;
        scanf("%d%d%d%d", &l1, &r1, &l2, &r2);
        
        if(get(l1, r1) == get(l2, r2))puts("Yes");
        else puts("No");
    }
    return 0;
}