Codeforces661 E1. Weights Division(easy version)(贪心+优先队列)

题目链接
思路
先计算每条边被计算的次数，然后贪心地每次减半能减少最多花费的边，直到小于等于S为止。
代码

#include
#define ll long long
#define LL long long
#define PB push_back
#define MP make_pair
using namespace std;
const int maxn=2e5+100;
const ll inf=1e18+10;
ll n,s,val[maxn],len[maxn];
struct node{
	ll u,to,v,id;
};
struct node2{
	ll ti,val,id;
};
bool operator<(node2 a, node2 b){
    return a.ti*(a.val-a.val/2)<b.ti*(b.val-b.val/2); 
}
vector<node>g[maxn];
ll dfs(int pre,int u){
	int sz=g[u].size();
	ll sum=0;
	if(sz==1&&u!=1)return 1;
	for(int i=0;i<sz;i++){
		ll to=g[u][i].to,v=g[u][i].v,id=g[u][i].id;
		if(to==pre)continue;
		val[id]=dfs(u,to);
		sum+=val[id];
	}
	return sum;
}
void slove(){
	scanf("%lld%lld",&n,&s);
	for(int i=1;i<=n;i++)g[i].clear(),val[i]=len[i]=0;
	for(int i=1;i<n;i++){
		val[i]=0;
		ll x,y,v;
		scanf("%lld%lld%lld",&x,&y,&v);
		g[x].PB(node{x,y,v,i});
		g[y].PB(node{y,x,v,i});
		len[i]=v;
	}
	dfs(0,1);
	ll sum=0;
	priority_queue<node2>q;
	for(int i=1;i<n;i++){
		sum+=val[i]*len[i];
		q.push(node2{val[i],len[i],i});
	}
	ll ans=0;
	while(sum>s){
		ans++;
		node2 x=q.top();
		q.pop();
		sum-=x.ti*(x.val-x.val/2);
		q.push(node2{x.ti,x.val/2,x.id});
	}
	printf("%lld\n",ans);
}
int main(){
	int t;
	scanf("%d",&t);
	while(t--){
		slove();
	}
	return 0;
}