POJ 2486 Apple Tree(树形DP)

/*
* source.cpp
*
*  Created on: Apr 7, 2014
*      Author: sangs
*/

#include <stdio.h>
#include <iostream>
#include <string>
#include <vector>
#include <memory.h>
#include <algorithm>
#include <math.h>
using namespace std;

int val[1000];
int dp[500][500][2];
vector<int> graph[1000];

/*
* dp[u][t][0] start from u and end at u, maximum income in t steps
* dp[u][t][1] .............not end at u, maximum income in .......
* dp[u][t][0] = max(dp[u][t][0], dp[u][t-2-k][0] + dp[v][k][0]) v is child of u
* dp[u][t][1] = max(dp[u][t][1], dp[u][t-1-k][0] + dp[v][k][1]) v is child of u and girl end at v
* dp[u][t][1] = max(dp[u][t][1], dp[u][t-2-k][1] + dp[v][k][0]) v is child of u and girl end at another child of u
*/
void solve_dp(int u, int pre, int vmax) {
for(int i = 0; i <= vmax; i ++) // at most k steps, not exactly k steps
dp[u][i][0] = dp[u][i][1] = val[u];

for(size_t i = 0; i < graph[u].size(); i ++) {
int v = graph[u][i];
if(v == pre) continue;

solve_dp(v, u, vmax);

for(int j = vmax;  j >= 0; j --) {
for(int k = 0; k <= j; k ++) {
dp[u][j+2][0] = max(dp[u][j][0], dp[u][j-k][0] + dp[v][k][0]);
dp[u][j+1][1] = max(dp[u][j][1], dp[u][j-k][0] + dp[v][k][1]);
dp[u][j+2][1] = max(dp[u][j][1], dp[u][j-k][1] + dp[v][k][0]);
}
}
}
}

int main() {
freopen("input.txt", "r", stdin);
int n, T;
while(scanf("%d%d", &n, &T) != EOF) {
for(int i = 1; i <= n; i ++)
scanf("%d", val+i);

for(int i =1; i <= n; i ++)
graph[i].clear();

memset(dp, 0, sizeof(dp));

for(int i = 1; i <= n-1; i ++) {
int from, to;
scanf("%d%d", &from, &to);
graph[from].push_back(to);
graph[to].push_back(from);
}

solve_dp(1, -1, T);
cout << dp[1][T][1] << endl;
}
return 0;
}