The xor-longest Path POJ

//#include<bits/stdc++.h>
//#pragma comment(linker, "/STACK:1024000000,1024000000") 
#include<stdio.h>
#include<algorithm>
#include<queue>
#include<string.h>
#include<iostream>
#include<math.h>
#include<set>
#include<map>
#include<vector>
#include<iomanip>
using namespace std;
#define ll long long
#define pb push_back
#define FOR(a) for(int i=1;i<=a;i++)
const int inf=0x3f3f3f3f;
const int maxn=1e5+9;  
const int maxnode=32*maxn;

struct EDGE{
	int v,w,next;
}G[maxn<<1];
int head[maxn],tot;
void init(){memset(head,-1,sizeof head);tot=0;}
void addedge(int u,int v,int w){
	++tot;G[tot]={v,w,head[u]};head[u]=tot;
}
int val[maxn];	//1路径异或到每个数的值
void dfs(int u,int fa,int dis){
	val[u]=dis;
	for(int i=head[u];~i;i=G[i].next){
		if(fa==G[i].v)continue;
		dfs(G[i].v,u,dis^G[i].w);
	}
}

int ch[maxnode][2];
int sz;
void trinit(){memset(ch[0],0,sizeof ch[0]);sz=1;}
void insert(int num){
	int u=0;
	for(int i=30;i>=0;i--){
		int v=(num>>i)&1;
		if(!ch[u][v]){
			memset(ch[sz],0,sizeof ch[sz]);
			ch[u][v]=sz++;
		}
		u=ch[u][v];
	}
}
int query(int num){
	int u=0,ans=0;
	for(int i=30;i>=0;i--){
		int v=((num>>i)&1)^1;
		if(ch[u][v]){
			ans|=(1<<i);
			u=ch[u][v];
		}else{
			u=ch[u][v^1];
		}
	}
	return ans;
}

int main(){
	int n;
	while(~scanf("%d",&n)){
		int u,v,w;
		init();
		for(int i=1;i<n;i++){
			scanf("%d%d%d",&u,&v,&w);
			u++;v++;
			addedge(u,v,w);addedge(v,u,w);
		}
		dfs(1,-1,0);
		trinit();
		int ans=0;
		for(int i=1;i<=n;i++){
			ans=max(ans,query(val[i]));
			insert(val[i]);
		}
		printf("%d
",ans);
	}
}

简单的树上异或，用到a^a=0的性质