HDU - 2586 How far away ？ （LCA最近公共祖先）

LCA入门问题，以后总结~~~

#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdio>
#include<string>
#include<string>
#include<vector>
#include<queue>
#include<stack>
#include<cmath>
#include<set>
#include<map>
using namespace std;
#define rep(i,a,n) for (int i=a;i<n;i++)
#define per(i,a,n) for (int i=n-1;i>=a;i--)
#define oo cout<<"!!!"<<endl;
typedef long long ll;
typedef unsigned long long ull;
#define ms(s) memset(s, 0, sizeof(s))
const int inf = 0x3f3f3f3f;
//head

const int maxn = 5e4+11;
int f[maxn][20],d[maxn],dist[maxn];
int ver[maxn*2],Next[maxn*2],edge[maxn*2],head[maxn],tot;
int t;

void add(int x,int y ,int z)
{
	ver[++tot] = y;edge[tot] = z;Next[tot] = head[x];head[x] = tot;
}

void bfs()
{
	queue<int>q;
	q.push(1);
	d[1] = 1;
	while(!q.empty())
	{
		int x = q.front();q.pop();
		for(int i = head[x];i;i = Next[i])
		{
			int y = ver[i];
			if(d[y])continue;
			d[y] = d[x] + 1;
			dist[y] = dist[x] + edge[i];
			f[y][0] = x;
			for(int j = 1;j<=t;j++)
				f[y][j] = f[f[y][j-1]][j-1];
			q.push(y);
		}
	}
}

int lca(int x,int y)
{
	if(d[x]>d[y])swap(x,y);
	for(int i = t;i>=0;i--) if(d[f[y][i]] >= d[x])
		y = f[y][i];
	if(x == y)return x;

	for(int i = t;i>=0;i--) if(f[x][i] != f[y][i])
		x = f[x][i],y = f[y][i];

	return f[x][0];
}


int main() 
{
	int T;cin>>T;

	while(T--)
	{
		int n,m;
		cin>>n>>m;
		t = (int)(log(n)/log(2))+1;
		rep(i,1,n+1)head[i] = d[i] = dist[t] = 0;
		tot = 0;

		rep(i,1,n)
		{
			int x,y,z;
			scanf("%d%d%d",&x,&y,&z);
			add(x,y,z);add(y,x,z);
		}
		bfs();
		rep(i,1,m+1)
		{
			int x,y;
			scanf("%d%d",&x,&y);
			printf("%d\n",dist[x]+dist[y]-2*dist[lca(x,y)]);
		}
	}
}