洛谷P1967 货车运输 AC代码

题目链接

#include <bits/stdc++.h>
using namespace std;
int n,m,q;
struct edge{
	int u;
	int v;
	int num;
}e[500005];
bool cmp(edge x,edge y){
	return x.num>y.num;
}
int f[100005];
int find(int x){
	if(f[x]==x)return x;
	return f[x]=find(f[x]);
}
struct line{
	int to;
	int num;
};
vector<line> ed[100005];
int st,eds;
int lg[100005],vis[100005],dep[100005];
int fa[100005][32],ln[100005][32];
void dofirst(int u,int fat){
	vis[u]=1;
	fa[u][0]=fat;
	dep[u]=dep[fat]+1;
	for(int i=1;i<=lg[dep[u]]-1;i++)fa[u][i]=fa[fa[u][i-1]][i-1],ln[u][i]=min(ln[u][i-1],ln[fa[u][i-1]][i-1]);
	for(int i=0;i<ed[u].size();i++){
		int v=ed[u][i].to;
		if(v==fat)continue;
		ln[v][0]=ed[u][i].num;
		dofirst(v,u);
	}
}
int lca(int x,int y){
	int ans=999999999;
	if(dep[x]<dep[y])swap(x,y);
	while(dep[x]>dep[y])ans=min(ans,ln[x][lg[dep[x]-dep[y]]-1]),x=fa[x][lg[dep[x]-dep[y]]-1];
	if(x==y)return ans;
	for(int j=lg[dep[x]]-1;j>=0;j--){
		if(fa[x][j]!=fa[y][j]){
			ans=min(ans,ln[x][j]);
			ans=min(ans,ln[y][j]);
			x=fa[x][j];
			y=fa[y][j];
		}
	}
	ans=min(ans,ln[x][0]);
	ans=min(ans,ln[y][0]);
	return ans;
}
int main() {
//	freopen("out.txt","w",stdout);
	memset(vis,0,sizeof(vis));
	scanf("%d%d",&n,&m);
	for(int i=1;i<=n;i++)f[i]=i,lg[i]=lg[i-1]+(i==1<<lg[i-1]);
	for(int i=1;i<=m;i++){
		scanf("%d%d%d",&e[i].u,&e[i].v,&e[i].num);
	}
	sort(e+1,e+m+1,cmp);
	int tot=0;
	for(int i=1;i<=m;i++){
		int fx=find(e[i].u),fy=find(e[i].v);
		if(fx!=fy){
			f[fx]=fy;
			ed[e[i].u].push_back((line){e[i].v,e[i].num});
			ed[e[i].v].push_back((line){e[i].u,e[i].num});
			tot++;
			if(tot==n-1)break;
			continue;
		}
	}
	dep[0]=0;
	for(int i=1;i<=n;i++){
		if(!vis[i])dofirst(i,0);
	}
	/*
	for(int i=1;i<=n;i++){
		cout<<i<<':'<<endl;
		cout<<"fa:";
		for(int j=0;j<=lg[n]-1;j++)cout<<fa[i][j]<<' ';
		cout<<endl;
		cout<<"ln:";
		for(int j=0;j<=lg[n]-1;j++)cout<<ln[i][j]<<' ';
		cout<<endl;
	}
	*/
	scanf("%d",&q);
	while(q--){
		scanf("%d%d",&st,&eds);
		if(find(st)!=find(eds)){
			printf("-1\n");
			continue;
		}else{
			printf("%d\n",lca(st,eds));
		}
	}
	return 0;
}