2013-2014 ACM-ICPC Pacific Northwest Regional Contest D.Delta Quadrant

题意略。

思路：

由于这是一颗无根树，我们可以贪心地来删去边。

详见代码：

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
const int maxn = 1e4 + 5;

struct edge{
    int from,to,len,id;
    edge(int a = 0,int b = 0,int c = 0,int d = 0){
        from = a,to = b,len = c,id = d;
    }
    bool operator< (const edge& e) const{
        return len < e.len;
    }
};

int indegree[maxn];
bool visit[maxn];
edge store[maxn];
priority_queue<edge> pq;

void init(){
    memset(visit,false,sizeof(visit));
    memset(indegree,0,sizeof(indegree));
    while(pq.size()) pq.pop();
}

int main(){
    int T;
    scanf("%d",&T);
    while(T--){
        int n,k;
        LL sum = 0;
        init();
        scanf("%d%d",&n,&k);
        int from,to,len;
        for(int i = 0;i < n - 1;++i){
            scanf("%d%d%d",&from,&to,&len);
            store[i] = edge(from,to,len,i);
            sum += len;
            indegree[from] += 1;
            indegree[to] += 1;
        }
        for(int i = 0;i < n - 1;++i){
            edge& e = store[i];
            if(indegree[e.from] == 1 || indegree[e.to] == 1){
                pq.push(e);
                visit[e.id] = true;
            }
        }
        LL ans = 0;
        for(int i = 0;i < k;++i){
            edge e = pq.top();
            pq.pop();
            --indegree[e.from];
            --indegree[e.to];
            ans += e.len;
            for(int j = 0;j < n - 1;++j){
                if(visit[j]) continue;
                edge ee = store[j];
                if(indegree[ee.from] == 1 || indegree[ee.to] == 1){
                    pq.push(ee);
                    visit[ee.id] = true;
                }
            }
        }
        ans = sum - ans;
        ans *= 2;
        printf("%lld\n",ans);
    }
    return 0;
}