如何表示状态？

dp[j]  前i只奶牛用for完成。

状态转移方程？

dp[j] = max(dp[j], dp[j−s[i]] + f[i])

初始状态？

memset(dp, −0x3f, sizeof(dp)); 负无穷

dp[400000] = 0;

代码

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

int n;
int s[405], f[405];
int dp[400005];
const int MR = 100000;

int main() {
    memset(dp, -0x3f, sizeof(dp));
	cin >> n;
	for (int i = 1; i <= n; i++) {
	    cin >> s[i] >> f[i];
	}
	dp[MR] = 0;
	for (int i = 1; i <= n; i++) {
		if (s[i] >= 0) {
		    for (int j = 2 * MR; j >= s[i]; j--) {
		        dp[j] = max(dp[j], dp[j - s[i]] + f[i]);
		    }
		} else {
		    for (int j = 0; j <= 2 * MR + s[i]; j++) {
		        dp[j] = max(dp[j], dp[j - s[i]] + f[i]);
		    }
		}
	}
	int ans = 0;
	for (int i = MR; i <= 2 * MR; i++)
		if (dp[i] >= 0)
			ans = max(ans, i + dp[i] - MR);
	cout << ans << endl;
    return 0;
}