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 + ;

struct edge{
    int from,to,len,id;
    edge(int a = ,int b = ,int c = ,int d = ){
        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,,sizeof(indegree));
    while(pq.size()) pq.pop();
}

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