题目链接：点击打开链接

#include <cstdio>
#include <algorithm>
#include <cstring>
#include <vector>
using namespace std;
typedef unsigned long long ll;
const int key = 1e9 + 7;
const int N = 2000 + 2;
ll xp[N], h[N];
char a[N], b[N], c[N];
int la, lb, lc;
vector<int> posl;
vector<ll> H;

ll Hash(int s, int len) {
	return h[s] - h[s + len] * xp[len];
}

void make(char* s, ll* h, int len) {
	xp[0] = 1;
	for (int i = 1; i < N; ++i)
		xp[i] = xp[i - 1] * key;
	h[len] = 0;
	for (int i = len - 1; i >= 0; --i)
		h[i] = h[i + 1] * key + s[i];
}

int main() {
	ll hb = 0, hc = 0;
	scanf("%s%s%s", a, b, c);
	la = strlen(a);
	lb = strlen(b);
	lc = strlen(c);
	for (int i = lb - 1; i >= 0; --i)
		hb = hb * key + b[i];
	for (int i = lc - 1; i >= 0; --i)
		hc = hc * key + c[i];
	make(a, h, la);
	for (int i = 0; i + lc <= la; ++i) 
		if (Hash(i, lc) == hc)
			posl.push_back(i);
	for (int i = 0; i + lb <= la; ++i)
		if (Hash(i, lb) == hb) {
			for (int j = 0; j < posl.size(); ++j) {
				if (posl[j] < i || posl[j] + lc < i + lb)
					continue;
				H.push_back(Hash(i, posl[j] + lc - i));
			}
		}
		sort(H.begin(), H.end());
		int ans = 0;
		if (H.size() > 0)
			ans = 1;
		for (int i = 1; i < H.size(); ++i)
			if (H[i] != H[i - 1])
				++ ans;
		printf("%d\n", ans); 
		return 0;
}

Codeforces 113B Petr# 字符串hash