(POJ) 1741 Tree

点分治

解题思路：点分治模板题，看懂上面那篇博客就能切啦。

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<cstring>
#include<queue>
#include<stack>
#include<map>
#include<set>
#include<cmath>
#include<sstream>
//#include<bits/stdc++.h>
#define il inline
#define pb push_back
#define fi first
#define se second
#define ms(_data,v) memset(_data,v,sizeof(_data))
#define sc(n) scanf("%d",&n)
#define SC(n,m) scanf("%d %d",&n,&m)
#define rep(i,a,b) for(int i=a;i<=b;++i)
#define drep(i,a,b)	for(int i=a;i>=b;--i)
using namespace std;
typedef long long ll;
const ll inf=0x3f3f3f3f;
const double PI=acos(-1.0);
const double eps=1e-9;
const int maxn=1e4+5;
int n,k,sz[maxn],root,mx,all,l,r;
ll dis[maxn],q[maxn],ans;
bool vis[maxn];
struct node{
	int to,w;
};
vector<node> mp[maxn];
il void getroot(int x,int fa){ //获取重心
	sz[x]=1;
	int num=0;
	for(int i=0;i<(int)(mp[x].size());++i){
		int nto=mp[x][i].to;
		if(vis[nto] || fa==nto) continue;
		getroot(nto,x);
		sz[x]+=sz[nto];
		num=max(num,sz[nto]);
	}
	num=max(num,all-num);
	if(num<mx){
		mx=num;
		root=x;
	}
}
il void getdis(int x,int fa){ //源点到该分支各点的距离
	q[++r]=dis[x];
	for(int i=0;i<(int)(mp[x].size());++i){
		int nto=mp[x][i].to,nw=mp[x][i].w;
		if(nto==fa || vis[nto]) continue;
		dis[nto]=dis[x]+nw;
		getdis(nto,x);
	}
}
il ll calc(int x,int v){ //计算满足的个数
	r=0,l=1,dis[x]=v;
	getdis(x,0);
	ll sum=0;
	sort(q+1,q+r+1);
	while(l<r){
		if(q[l]+q[r]<=k) sum+=r-l,l++;
		else r--;
	}
	return sum;
}
il void dfs(int x){ 
	ans+=calc(x,0);
	vis[x]=1;
	for(int i=0;i<(int)(mp[x].size());++i){
		int nto=mp[x][i].to,nw=mp[x][i].w;
		if(vis[nto]) continue;
		ans-=calc(nto,nw); //减去不和条件的
		all=sz[x];
		mx=inf;
		getroot(nto,0);
		dfs(root);
	}
}
int main(){
	while(SC(n,k)!=EOF){
		if(n==0 && k==0) break;
		all=n,ans=0;
		int x,y,z;
		for(int i=1;i<=n-1;++i){
			sc(x),sc(y),sc(z);
			mp[x].pb(node{y,z});
			mp[y].pb(node{x,z});
		}
		mx=inf;
		getroot(1,0);
		dfs(root);
		cout<<ans<<endl;
		for(int i=0;i<=n+5;++i){
			mp[i].clear();
			vis[i]=0;
		}	
	}
	return 0;
}