P3379 LCA(模板)

luogu

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<string>
#include<cmath>
#include<vector>
#define NN 500000
using namespace std;
int n,m,s;
//vector <int> a[NN+2];
int num[2*NN+9],head[NN+9],nxt[2*NN+9],cnt=0;
int p[NN+2][20],deep[NN+2];
inline int Read(){
    int x=0,f=1;char c=getchar();
    while(c>'9'||c<'0') {if(c=='-') f=-1;c=getchar();}
    while(c>='0'&&c<='9') {x=x*10+c-'0'; c=getchar();}
    return x*f;
}
void dfsfa(int u)
{
    for(int i=head[u];i;i=nxt[i])
     if(!p[num[i]][0]){
        int x=num[i];
        p[x][0]=u;
        deep[x]=deep[u]+1;
        dfsfa(x);
     }
}
void fa2()
{
    for(int j=1;(1<<j)<=n;j++)
     for(int i=1;i<=n;i++)
      if(p[i][j-1]!=-1){
        p[i][j]=p[p[i][j-1]][j-1];
      }
}
int LCA(int a,int b)
{
    if(deep[a]<deep[b])swap(a,b);
    int x;
    for(x=0;(1<<x)<=deep[a];x++);

    x--;
    for(int j=x;j>=0;j--)
     if(deep[a]-(1<<j)>=deep[b])
      a=p[a][j];               //a,b 到了同一高度 
    if(a==b)return a;

    for(int j=x;j>=0;j--){//找 
        if(p[a][j]!=-1&&p[a][j]!=p[b][j])
        {
            a=p[a][j];
            b=p[b][j];
        }
    }
    return p[a][0];
} 
int main()
{
    scanf("%d%d%d",&n,&m,&s);
    for(int i=1;i<=n-1;i++)
    {
        int x,y;
        x=Read();
        y=Read();
        //scanf("%d%d",&x,&y);
        cnt++;
        num[cnt]=x;
        nxt[cnt]=head[y];
        head[y]=cnt;

        cnt++;
        num[cnt]=y;
        nxt[cnt]=head[x];
        head[x]=cnt; 
    }
    deep[s]=0;p[s][0]=-1;
    dfsfa(s);
    fa2();
    for(int i=1;i<=m;i++){
        int x,y;
        x=Read();
        y=Read();
        //scanf("%d%d",&x,&y);
        printf("%d
",LCA(x,y));
    }
    return 0;
}