LCA 计算最近的公共祖先（裸版） tarjin的离线版

学习链接http://www.cnblogs.com/JVxie/p/4854719.html

 

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
using namespace std;
#define maxn 100010
typedef long long ll;
vector<int>s[maxn],q[maxn];
vector<ll>w[maxn];
int n,m,fa[maxn],k[100][100],a[maxn],b[maxn];
bool vis[maxn];
inline int read(){
    int num=0,f=1; char c=getchar();;
    while(!isdigit(c)){if(c=='-') f=-1; c=getchar();}
    while(isdigit(c)){num=(num<<1)+(num<<3)+(c^48); c=getchar();}
    return num*f;
}
int find(int x){
    if(fa[x]!=x) fa[x]=find(fa[x]);
    return fa[x];
}
inline int un(int a,int b){
    int A=find(a),B=find(b);
    fa[A]=B;
}
void lca(int x){
    vis[x]=1;
    int num=s[x].size();
    for(int i=0;i<num;i++){
        int u=s[x][i];
        if(!vis[u]){
            lca(u);
            un(u,x);//和并查集不一样这里必须有顺序 
        }
    }
    num=q[x].size();
    for(int i=0;i<num;i++){
        int e=q[x][i];
        if(vis[e]){
            k[x][e]=find(e); 
            k[e][x]=k[x][e];//注意双向更新 
        }
    }
}
inline int in(){
    n=read(); m=read();
    for(int i=1;i<=n;i++) fa[i]=i;
    for(int i=1;i<n;i++){
        ll u,v,w;
        u=read(); v=read();
        s[u].push_back(v);
        s[v].push_back(u);
    }
    for(int i=1;i<=m;i++){
        a[i]=read(); b[i]=read();
        q[a[i]].push_back(b[i]);
        q[b[i]].push_back(a[i]);
    }
    lca(1);
}
inline int out(){
    for(int i=1;i<=m;i++) cout<<k[a[i]][b[i]]<<endl;
}
int main(){
    in();
    out();
}
//9 2
//1 2
//1 3
//2 4
//2 5
//5 7
//5 8
//7 9
//3 6
//2 3
//7 8