hdu 5148 Cities(树形dp)

#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>

using namespace std;

typedef pair<int, int> pii;
typedef long long ll;
const int maxn = 2005;

int N, K;
ll ans, dp[maxn][55];
vector<pii> g[maxn];

void cmin(ll& v, ll x) {
if (v == -1 || v > x)
v = x;
}

void init () {
scanf("%d%d", &N, &K);

ans = -1;
memset(dp, -1, sizeof(dp));
for (int i = 1; i <= N; i++)
g[i].clear();

int a, b, c;
for (int i = 1; i < N; i++) {
scanf("%d%d%d", &a, &b, &c);
g[a].push_back(make_pair(b, c));
g[b].push_back(make_pair(a, c));
}
}

void dfs(int u, int f) {
dp[u][1] = 0;

for (int i = 0; i < g[u].size(); i++) {
int v = g[u][i].first;
int w = g[u][i].second * 2;
if (v == f) continue;
dfs(g[u][i].first, u);
for (int k = K - 1; k; k--) {
if (dp[u][k] == -1) continue;
for (int j = 1; j + k <= K; j++) {
if (dp[v][j] == -1) continue;
cmin(dp[u][k+j], dp[u][k] + dp[v][j] + w * (K - j) * j);
}
}
}
if (dp[u][K] != -1)
cmin(ans, dp[u][K]);
}

int main () {
int cas;
scanf("%d", &cas);
while (cas--) {
init();
dfs(1, 0);
printf("%I64d\n", ans);
}
return 0;
}