POJ1330Nearest Common Ancestors最近公共祖先LCA问题

用的离线算法Tarjan

该算法的详细解释请戳

http://www.cnblogs.com/Findxiaoxun/p/3428516.html

做这个题的时候，直接把1470的代码copy过来，改了改输入输出。这个的难度比那个低。

#include<cstdio>
#include<algorithm>
#include<cstring>
#include<vector>
using namespace std;
;
int father[MAXN],ancestor[MAXN];
bool visit[MAXN];
int ans[MAXN];
vector<int> map[MAXN];//save the tree
int n,t,root,sx,sy;
bool indegree[MAXN];//the indegree to find the root
int getfather(int v){//path compression
    if(father[v]==v)return v;
    return father[v]=getfather(father[v]);
}
void aunion(int u,int v){
    int fv=getfather(v),fu=getfather(u);
    father[fv]=fu;
}
bool isit(int a,int b){
    if(a==sx&&b==sy)return true;
    return false;
}
void LCA(int id){
    int len=map[id].size();
    int son;
    ;i<len;i++){
        son=map[id][i];
        LCA(son);
        aunion(id,son);
    }
    visit[id]=;
    if(visit[sy]&&id==sx){
        printf("%d\n",father[getfather(sy)]);
        return;
    }else{//attention:this way
        if(visit[sx]&&id==sy){
            printf("%d\n",father[getfather(sx)]);
            return;
        }
    }

}
void init(){
    int x,y,z;
    scanf("%d",&n);
    //initialize all the vars
    ;i<=n;i++){
        map[i].clear();
    }
    memset(visit,,sizeof(visit));
    memset(ans,,sizeof(ans));
    memset(indegree,,sizeof(indegree));
    ;i<=n;i++)father[i]=i;
    ;i<n-;i++){
        scanf("%d%d",&x,&y);
        indegree[y]=;
        map[x].push_back(y);
    }
    scanf("%d%d",&sx,&sy);
    ;i<=n;i++)if(!indegree[i])root=i;//find the root;warning:the 0
}
int main(){
    int  t;
    scanf("%d",&t);
    while(t--){
        init();
        LCA(root);
    }
    ;
}