【NOIP2013提高组】货车运输

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做法：克鲁斯卡尔+倍增LCA

#include<cstdio>
#include<algorithm>
using namespace std;
struct street {int u,v,z;}a[50010];
struct node {int v,fr,z;}e[20010];
int tail[10010],fa[10010],dep[10010];
int f[10010][14],g[10010][14];
int cnt=0,n,m,p,minn;

inline int read()
{
	int x=0;char c=getchar();
	while (c<'0' || c>'9') c=getchar();
	while (c>='0' && c<='9') x=x*10+c-48,c=getchar();
	return x;
}

void add(int u,int v,int z) {e[++cnt]=(node){v,tail[u],z}; tail[u]=cnt;}

int cmp(street x,street y) {return x.z>y.z;}

int gf(int x) {return !fa[x] ? x:fa[x]=gf(fa[x]);}

void dfs(int x)
{
	for (int p=tail[x];p;p=e[p].fr)
		if (!f[e[p].v][0])
		{
			dep[e[p].v]=dep[x]+1;
			f[e[p].v][0]=x;
			g[e[p].v][0]=e[p].z;
			dfs(e[p].v);
		}
}

int LCA(int x,int y)
{
	minn=100010;
	if (dep[x]<dep[y]) swap(x,y);
	for (int i=13;i>=0;i--)
		if (dep[x]-dep[y]>=(1<<i))
			minn=min(minn,g[x][i]),x=f[x][i];
	if (x==y) return x;
	for (int i=13;i>=0;i--)
		if (f[x][i]!=f[y][i])
		{
			minn=min(minn,min(g[x][i],g[y][i]));
			x=f[x][i],y=f[y][i];
		}
	if (f[x][0]!=f[y][0]) return 0;
	else
	{
		minn=min(minn,min(g[x][0],g[y][0]));
		return f[x][0];
	}
}

int main()
{
//	freopen("truck.in","r",stdin);
//	freopen("truck.out","w",stdout);
	n=read(),m=read();
	for (int i=1;i<=m;i++)
		a[i]=(street){read(),read(),read()};
	sort(a+1,a+m+1,cmp);
	for (int i=1;i<=m;i++)
		if (gf(a[i].u)!=gf(a[i].v)) 
		{
			fa[gf(a[i].u)]=gf(a[i].v);
			add(a[i].u,a[i].v,a[i].z);
			add(a[i].v,a[i].u,a[i].z);
		}
	dfs(1);
	for (int j=1;j<=13;j++)
		for (int i=1;i<=n;i++)
		{
			f[i][j]=f[f[i][j-1]][j-1];
			g[i][j]=min(g[i][j-1],g[f[i][j-1]][j-1]);
		}
	p=read();
	for (int i=1,lca;i<=p;i++)
	{
		lca=LCA(read(),read());
		if (!lca || minn==100010) puts("-1");
		else printf("%d\n",minn);
	}
	return 0;
}