Submission #2225795

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Source Code Expand

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define rep1(i,n) for(int i=1;i<=(int)(n);i++)

using namespace std;
typedef long long int lli;

const lli MOD = 1e9 + 7;
lli N, M;

int main() {
	cin >> N >> M;
	//でかい方をm,小さいほうをnに
	lli m = N, n = N;
	if (N<M) m = M;
	if (N>M) n = M;
	lli ans = 0;
	//同じ数,差が1,それ以外で場合分け
	if (m == n) {
		//この場合答えは2*n!*n!
		ans = 1;
		rep1(i, n) ans = (ans*i) % MOD;
		ans = (ans*ans) % MOD;
		ans = (2 * ans) % MOD;
	}
	else if (m - n == 1) {
		//この場合答えは(n+1)*n!*n!
		ans = 1;
		rep1(i, n) ans = (ans*i) % MOD;
		ans = (ans*ans) % MOD;
		ans = ((n + 1)*ans) % MOD;
	}
	cout << ans;
}

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