LCA模板

来源：互联网发布：手机淘宝怎么撤销投诉编辑：程序博客网时间：2024/06/03 13:15

代码为nkoj1536--【Usaco Oct08 Gold】奶牛串门(Pasture Walking)

#include<cstdio>#include<iostream>#include<algorithm>#include<cstring>#include<cstdlib>#include<cmath>using namespace std;int father[10005][50];int dep[10005];int n,m=0;int S;int root;struct line{int from;int to;int len;};line edge[1000005];int len[100005];int last[10005],_next[1000005];void add_edge(int x,int y,int l){m++;edge[m].from=x;edge[m].to=y;edge[m].len=l;_next[m]=last[x];last[x]=m;}bool mark[10005];void dfs(int x,int fa){int i,h,v;father[x][0]=fa;dep[x]=dep[father[x][0]]+1;int k=ceil(log(dep[x])/log(2));for(i=1;i<=k;i++){father[x][i]=father[father[x][i-1]][i-1];}for(h=last[x];h;h=_next[h]){v=edge[h].to;if(v==fa)continue;len[v]=len[x]+edge[h].len;dfs(v,x);}}void go_up(int &v,int p){int i;for(i=0;i<S;i++){if(p&(1<<i))v=father[v][i];}}int lca(int x,int y){int i,k;if(dep[x]<dep[y])swap(x,y);k=dep[x]-dep[y];go_up(x,k);if(x==y)return x;int s=ceil(log(dep[x])/log(2));for(i=s;i>=0;i--){if(father[x][i]!=father[y][i]){x=father[x][i];y=father[y][i];}}return father[x][0];}int main(){int m;cin>>n>>m;int i,j,k;S=ceil(log(n)/log(2));for(i=1;i<n;i++){int x,y,l;scanf("%d%d%d",&x,&y,&l);add_edge(x,y,l);add_edge(y,x,l);}dfs(1,0);while(m--){int x,y,t;scanf("%d%d",&x,&y);t=lca(x,y);printf("%d\n",len[x]+len[y]-2*len[t]);}}

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