zoj3905 贪心dp

n个蛋糕选一半，使得val最大。dp[i][j]表示前i个蛋糕选j个最大的val，则dp[i][j] = max(dp[i-1][j] , dp[i-1][j-1] + cake[i].a) , j <= i/2; 递推前按b排序

#include <bits/stdc++.h>

using namespace std;
#define MAXN 800
int dp[MAXN+10][MAXN+10];
struct cake
{
    int a , b;
}arr[MAXN+10];

bool cmp(cake c1 , cake c2)
{
    return c1.b > c2.b;
}

int main()
{
    int t , n;
    scanf("%d" , &t);
    while(t--)
    {
        scanf("%d" , &n);
        for(int i = 1 ; i <= n ; i ++)
        {
            scanf("%d %d" , &arr[i].a , &arr[i].b);
        }
        sort(arr + 1, arr + n + 1, cmp);
        memset(dp , 0 , sizeof(dp));
        for(int i = 1 ; i <= n ; i ++)
        {
            for(int j = 1 ; j <= i / 2 ; j ++)
            {
                dp[i][j] = max(dp[i-1][j] , dp[i-1][j-1] + arr[i].a);
            }
        }
        printf("%d\n" , dp[n][n/2]);
    }
    return 0;
}