백준 1328번 C++

#include <iostream>
#include <algorithm>
#include <cstring>

using namespace std;
const int MAX = 101;
const int MOD = 1000000007;
int n, l, r, answer = 0;
long long building[MAX][MAX][MAX];

long long calway(int num, int left, int right) {
	if (num == n && left == l && right == r)
		return 1;

	if (num > n)
		return 0;

	if (left > l || right > r)
		return 0;

	long long &answer = building[num][left][right];
	if (answer != -1)
		return answer;

	answer = ( calway(num + 1, left + 1, right) + calway(num + 1, left, right + 1) + calway(num+1,left,right) * (num-1)) % MOD;
	
	return answer;
}


int main(void) {
	cin >> n >> l >> r;

	memset(building, -1, sizeof(building));
	cout << calway(1, 1, 1) << endl;
	return 0;
}