[AcWing 11] 背包问题求方案数

#include<iostream>
#include<cstring>

using namespace std;

const int N = 1010, mod = 1e9 + 7;
int n, m;
int f[N], g[N];

int main()
{
	cin >> n >> m;
	memset(f, -0x3f, sizeof f);
	f[0] = 0;
	g[0] = 1;
	for (int i = 1; i <= n; i ++) {
		int v, w;
		cin >> v >> w;
		for (int j = m; j >= v; j --) {
			int maxv = max(f[j], f[j - v] + w);
			int cnt = 0;
			if (maxv == f[j])	cnt += g[j];
			if (maxv == f[j - v] + w)	cnt += g[j - v];
			g[j] = cnt % mod;
			f[j] = maxv;
		}
	}
	int res = 0, ans = 0;
	for (int i = 0; i <= m; i ++)	res = max(res, f[i]);
	for (int i = 0; i <= m; i ++)
		if (f[i] == res)
			ans = (ans + g[i]) % mod;
	cout << ans << endl;
	return 0;
}