Submission #2212934

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Source Code Expand

#include<iostream>
#include<string>
#include<algorithm>
#include<vector>
#include<queue>
#include<functional>
#include<cmath>
#include<random>
#include<map>
using namespace std;
#define int long long
const long long mod = 1000000007;

int kaijo[200005];
int ikaijo[200005];
int modp(int x, int n, int md) {
	if (n == 0)return 1;
	int res = modp(x*x%md, n / 2, md);
	if (n & 1)res = res*x%mod;
	return res;
}

signed main() {
	int h, w, a, b; cin >> h >> w >> a >> b;
	kaijo[0] = 1;
	for (int i = 1; i <= h+w; i++)kaijo[i] = (kaijo[i - 1] * i)%mod;
	for (int j = 0; j <= h + w; j++) {
		ikaijo[j] = modp(kaijo[j], mod - 2, mod);
	}
	int ans = 0;
	for (int i =  b + 1; i <= w; i++) {
		int x = h - a, y = i, X = a, Y = w-i+1;
		int cm = (kaijo[x + y - 2] * ikaijo[x - 1] %mod* ikaijo[y - 1])%mod;
		int CM = (kaijo[X + Y - 2] * ikaijo[X - 1]%mod * ikaijo[Y - 1])%mod;
		ans += ((cm * CM) % mod);
		ans %= mod;
			}
	cout << ans << endl;
}

Submission Info

Judge Result