这道题最重要的不仅是hash这种算法，更要学会利用好STL中的<map>才行。

将连续的L个字符经过hash赋值，最后线性判断。其中的判断步骤用到了map的插入特性。

#include <iostream>#include <cstdio>#include <algorithm>#include <cstring>#include <map>using namespace std;#define maxn 500010#define ull unsigned long longull sum[maxn];map<ull, bool> mp;ull l, m;int solve(ull be, ull len){    int ret = 0;    mp.clear();    for(ull i = be; i < len; i += l)    {        if(mp[sum[i]])        {            while(sum[be] != sum[i])            {                mp[sum[be]] = 0;                be += l;            }            mp[sum[be]] = 0;            be += l;        }        mp[sum[i]] = 1;        if((i - be) / l == m - 1)        {            ret++;            mp[sum[be]] = 0;            be += l;        }    }    return ret;}int main(){    char c[maxn];    while(~scanf("%d%d", &m, &l))    {        scanf("%s", c);        ull len = strlen(c);        ull base = 31;        ull bit = 1;        ull tmp = 0;        for(ull i = 0; i < l; i++)        {            tmp = tmp * base + c[i] - ‘a‘;            bit *= base;        }        int ans = 0;        sum[l - 1] = tmp;        for(ull i = l; i < len; i++)        {            sum[i] = sum[i - 1] * base + c[i] - ‘a‘  - bit * (c[i - l] - ‘a‘);        }        for(ull i = l - 1; i < l * 2 - 1; i++)        {            ans += solve(i, len);        }        printf("%d\n", ans);    }}