HDU 1561

树上背包，如果选择子树父节点必须选，所以边界初始化要注意一下。具体分析待整理。

#include <cstdio>
#include <cstring>
using namespace std;

#define MAXV    205
#define MAXE    (MAXV-1)

int Vefw[MAXE], Veh[MAXV], Vet[MAXE], Veptr;

#define addedge(s,t) ({
    Vefw[Veptr] = Veh[s], Vet[Veptr] = t; 
    Veh[s] = ++Veptr; })

int N;
int dp[MAXV][MAXV+1];
#define Vtrs(x)        dp[x][1]

int solve(int s)
{
    for(int i=N; i>1; --i)
        dp[s][i] = 0;
    int nsum = 1;

    for(int e = Veh[s]; e; e = Vefw[e]) {
        int t = Vet[--e];
        int tsum = solve(t);

        for(int i=nsum + tsum; i>0; --i) {
            for(int j=1; j<=tsum; ++j) {
                if (i - j <= 0) break;
                if (dp[s][i] < dp[s][i-j] + dp[t][j])
                    dp[s][i] = dp[s][i-j] + dp[t][j];
            }
        }

        nsum += tsum;
    }
    return nsum;
}

int M;

int main(void)
{
    freopen("hdu1561.txt", "r", stdin);
    while(scanf("%d%d", &N, &M), N && M) {
        ++N, Veptr = 0;
        for(int t=1; t<N; ++t) {
            int s;
            scanf("%d%d",&s, &Vtrs(t));
            addedge(s, t);
        }
        solve(0);
        printf("%d
", dp[0][M+1]);
        memset(Veh, 0, sizeof(int) * N);
    }
    return 0;
}

10738682

2014-05-14 14:41:32

Accepted

1561

0MS

372K

1040 B

G++