https://www.lydsy.com/JudgeOnline/problem.php?id=3732
C++版本一
题解:最近公共祖先+最小生成树+并查集
/*
*@Author: STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
#define endl "\n"
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=100000+10;
const int M=100000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,p,l,r,u,v,q;
int ans,cnt,flag,temp,sum;
int pre[N],dp[23][N],dep[N],maxl[23][N];
bool vis[N];
char str;
int find(int x){return pre[x]==x?x:pre[x]=find(pre[x]);}
struct node{
int u,v,w;
bool operator < (const node &S)const{
return w<S.w;
}
}e[N],x;
vector<node>G[N];
void dfs(int u){
vis[u]=1;
for(int i=0,j=G[u].size();i<j;i++){
int v=G[u][i].v;
if(!vis[v]){
maxl[0][v]=G[u][i].w;
dp[0][v]=u;
dep[v]=dep[u]+1;
dfs(v);
}
}
}
void ST(){
for(int i=0;i<21;i++){
for(int j=1;j<=n;j++){
dp[i+1][j]=dp[i][dp[i][j]];
maxl[i+1][j]=max(maxl[i][j],maxl[i][dp[i][j]]);
//cout<<maxl[i+1][j]<<endl;
}
}
}
int LCA(int x,int y){
int maxans=1;
if(dep[x]<dep[y])
swap(x,y);
while(dep[x]!=dep[y]){
maxans=max(maxans,maxl[(int)log2(dep[x]-dep[y])][x]);
x=dp[(int)log2(dep[x]-dep[y])][x];
}
if(x==y)
return maxans;
for(int i=log2(dep[x]);i>=0;i--){
if(dp[i][x]!=dp[i][y]){
maxans=max(maxans,max(maxl[i][x],maxl[i][y]));
x=dp[i][x];
y=dp[i][y];
}
}
maxans=max(maxans,max(maxl[0][x],maxl[0][y]));
return maxans;
}
int main()
{
#ifdef DEBUG
freopen("input.in", "r", stdin);
//freopen("output.out", "w", stdout);
#endif
//ios::sync_with_stdio(false);
//cin.tie(0);
//cout.tie(0);
//scanf("%d",&t);
//while(t--){
scanf("%d%d%d",&n,&m,&k);
for(int i=1;i<=m;i++){
scanf("%d%d%d",&e[i].u,&e[i].v,&e[i].w);
}
sort(e+1,e+m+1);
for(int i=1;i<=n;i++)pre[i]=i;
for(int i=1;i<=m;i++){
int tx=find(e[i].u);
int ty=find(e[i].v);
if(tx!=ty){
x=e[i];
G[e[i].u].push_back(x);
swap(x.u,x.v);
G[e[i].v].push_back(x);
pre[tx]=ty;
}
}
for(int i=1;i<=n;i++){
if(!vis[i]){
dfs(i);
}
}
ST();
while(k--){
scanf("%d%d",&u,&v);
int tx=find(u);
int ty=find(v);
if(tx!=ty){
cout<<-1<<endl;
}else{
cout<<LCA(u,v)<<endl;
}
}
//}
#ifdef DEBUG
printf("Time cost : %lf s\n",(double)clock()/CLOCKS_PER_SEC);
#endif
//cout << "Hello world!" << endl;
return 0;
}