货车运输
https://www.luogu.org/problemnew/show/P1967
題解：最大瓶頸路徑問題
并查集+最大生成樹+LCA
/* *@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]=min(maxl[i][j],maxl[i][dp[i][j]]);//cout<<maxl[i+1][j]<<endl;}} } int LCA(int x,int y){int maxans=INF;if(dep[x]<dep[y])swap(x,y);while(dep[x]!=dep[y]){maxans=min(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=min(maxans,min(maxl[i][x],maxl[i][y]));x=dp[i][x];y=dp[i][y];}}maxans=min(maxans,min(maxl[0][x],maxl[0][y]));return maxans; } 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(t--){scanf("%d%d",&n,&m);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=0;i<21;i++){for(int j=0;j<N;j++){maxl[i][j]=INF;}}for(int i=1;i<=n;i++){if(!vis[i]){dfs(i);}}ST();scanf("%d",&q);while(q--){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 DEBUGprintf("Time cost : %lf s\n",(double)clock()/CLOCKS_PER_SEC); #endif//cout << "Hello world!" << endl;return 0; }?
總結
