Connections between cities

http://acm.hdu.edu.cn/showproblem.php?pid=2874

题解：LCA

参考文章： https://blog.csdn.net/weixin_43272781/article/details/88797088

/*
*@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,c;
int ans,cnt,flag,temp,sum,num;
int pre[N];
bool vis[N];
int dep[N];
int dp[N][21];
int dist[N];
int que[N];
int first[N];
char str;
struct node{int v,w;
}x;
struct query{int e,id;
}y;
vector<node>G[N];
int find(int x){return pre[x]==x?x:pre[x]=find(pre[x]);}
void marge(int u,int v){int tu=find(u);int tv=find(v);if(tu!=tv){pre[tv]=tu;}
}
void dfs(int u,int deep){vis[u]=1;que[++num]=u;//num在此处相当于dfs_clockfirst[u]=num;//表示第一次走的编号dep[num]=deep;for(int i=0,j=G[u].size();i<j;i++){int v=G[u][i].v;int w=G[u][i].w;if(!vis[v]){dist[v]=dist[u]+w;dfs(v,deep+1);que[++num]=u;dep[num]=deep;}}
}
void ST(int n){for(int i=1;i<=n;i++){dp[i][0]=i;}for(int i=0;(1<<i)<n;i++){for(int j=1;j+(1<<i)<n;j++){int a=dp[j][i],b=dp[j+(1<<i)][i];dp[j][i+1]=dep[a]<dep[b]?a:b;}}
}
int RMQ(int l,int r){k=log2(r-l+1);int a=dp[l][k],b=dp[r-(1<<k)+1][k];return dep[a]<dep[b]?a:b;
}
int LCA(int u,int v){int x = first[u] , y = first[v];if(x > y) swap(x,y);int res = RMQ(x,y);return que[res];
}
void init(){for(int i=1;i<=n;i++){G[i].clear();pre[i]=i;}memset(vis,0,sizeof(vis));memset(dep,0,sizeof(dep));memset(dist,0,sizeof(dist));memset(dp,0,sizeof(dp));memset(que,0,sizeof(que));cnt=0,num=0;
}
int main()
{
#ifdef DEBUGfreopen("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(~scanf("%d%d%d",&n,&m,&c)){init();for(int i=1;i<=m;i++){scanf("%d%d%d",&u,&v,&k);x.v=v;x.w=k;G[u].push_back(x);x.v=u;G[v].push_back(x);marge(u,v);}for(int i=1;i<=n;i++){if(pre[i]==i){dist[i]=0;dfs(i,1);}}ST(2*n-1);for(int i=1;i<=c;i++){scanf("%d%d",&u,&v);if(find(u)==find(v)){int lca=LCA(u,v);cout<<dist[u]+dist[v]-2*dist[lca]<<endl;}else{cout<<"Not connected"<<endl;}}}#ifdef DEBUGprintf("Time cost : %lf s\n",(double)clock()/CLOCKS_PER_SEC);
#endif//cout << "Hello world!" << endl;return 0;
}

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