bzoj1602[Usaco2008 Oct]牧场行走(lca模版)

Lca裸题

#include<iostream>#include<cstdio>#include<cmath>#include<cstring>#include<algorithm>#define fo(i,a,b) for(int i=a;i<=b;i++)#define fod(i,a,b) for(int i=a;i>=b;i--)using namespace std;const int N=1e3+10;int dep[N],f[N][10],dis[N],n,q,len=0,last[N];struct Edge{int to,next,val;Edge(int to=0,int next=0,int val=0):to(to),next(next),val(val){}}e[N<<1];void add_edge(int u,int v,int w){e[++len]=Edge(v,last[u],w);last[u]=len;}void dfs(int u,int fa){    for(int i=1;i<=9;i++) {        if(dep[u]<(1<<i))break;        f[u][i]=f[f[u][i-1]][i-1];    }    for(int i=last[u];i;i=e[i].next){        int id=e[i].to;        if(id==fa)continue;        dep[id]=dep[u]+1;dis[id]=dis[u]+e[i].val;        f[id][0]=u;        dfs(id,u);    }}int lca(int x,int y){    if(dep[x]<dep[y])swap(x,y);    int d=dep[x]-dep[y];    for(int i=0;i<=9;i++){        if(d&(1<<i))x=f[x][i];      }    for(int i=9;i+1;i--) {        if(f[x][i]!=f[y][i])             x=f[x][i],y=f[y][i];    }    if(x==y)return x;    else return f[x][0];}int main(){    scanf("%d%d",&n,&q);    for(int u,v,w,i=1;i<n;i++) {        scanf("%d%d%d",&u,&v,&w);        add_edge(u,v,w);add_edge(v,u,w);    }    dfs(1,0);    for(int x,y,i=1;i<=q;i++) {        scanf("%d%d",&x,&y);        printf("%d\n",dis[x]+dis[y]-2*dis[lca(x,y)]);    }    return 0;}