为什么多重背包不二进制优化能过，二进制优化会 WA。

代码（优化）：

#include <bits/stdc++.h>
using namespace std;
#define N 10005

int n, k, dp[N];

int main() {
	scanf("%d%d", &k, &n); dp[0] = 1;
	for (int i = 0; (1 << i) <= n; i++)
		for (int cnt = 1; cnt * (1 << i) <= n && cnt <= k; cnt <<= 1)
			for (int j = n; j >= cnt * (1 << i); j--)
				dp[j] = (dp[j] + dp[j - cnt * (1 << i)]) % 1000000007;
	printf("%d\n", dp[n]);
	return 0;
}

不优化：

#include <bits/stdc++.h>
using namespace std;
#define N 10005

int n, k, dp[N];

int main() {
	scanf("%d%d", &k, &n); dp[0] = 1;
	for (int i = 0; (1 << i) <= n; i++)
		for (int j = n; j; j--)
		    for (int cnt = 1; cnt <= k && cnt * (1 << i) <= j; cnt++)
				dp[j] = (dp[j] + dp[j - cnt * (1 << i)]) % 1000000007;
	printf("%d\n", dp[n]);
	return 0;
}