PKU 2184 Cow Exhibition 01背包

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <string>
#include <queue>
#include <stack>
#include <vector>
#include <map>
#include <set>
#include <functional>
#include <cctype>
#include <time.h>

using namespace std;

typedef pair<int, int> PII;

const int INF = 1e6;
const int MAXM = 1e5+5;
const int MAXN = 111;

PII a[MAXN];
int dp[MAXM];
int n;

int main() {
    #ifdef Phantom01
        freopen("PKU2184.txt", "r", stdin);
    #endif //Phantom01

    while (scanf("%d", &n)!=EOF) {
        int sum = 0;
        for (int i = 0; i < n; i++) {
            scanf("%d%d", &a[i].first, &a[i].second);
            if (a[i].first>0) sum += a[i].first;
        }
        sort(a, a+n);
        for (int i = 0; i <= sum; i++) dp[i] = -INF;
        dp[0] = 0;
        for (int i = n-1; i >= 0; i--) {
            int f = a[i].first, s = a[i].second;
            if (f<0 && s<0) continue;
            if (f>=0) {
                for (int j = sum-f; j >= 0; j--) {
                    dp[j+f] = max(dp[j+f], dp[j]+s);
                }
            } else {
                for (int j = -f; j <= sum; j++) {
                    dp[j+f] = max(dp[j+f], dp[j]+s);
                }
            }
        }
        int ans = 0;
        for (int i = 0; i <= sum; i++) if (dp[i]>=0) {
            ans = max(ans, i+dp[i]);
        }
        printf("%d\n", ans);
    }

    return 0;
}