POJ 1330:Nearest Common Ancestors【lca】

题目大意：唔就是给你一棵树和两个点，问你这两个点的LCA是什么

思路:LCA的模板题，要注意的是在并查集合并的时候并不是随意的，而是把叶子节点合到父节点上

#include<cstdio>

#include<string.h>

#include<iostream>

#include<algorithm>

#include<math.h>

#define maxn 10002

#define MOD 1000000007

using namespace std;

int head[maxn],point[maxn],next[maxn],father[maxn];

int now=0,in[maxn],finish=0;

bool visit[maxn];

inline int read()

{

int x=0;char ch=getchar();

while(ch<'0'||ch>'9')ch=getchar();

while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}

return x;

}

void add(int x,int y)

{

next[++now]=head[x];

head[x]=now;

point[now]=y;

}

int find(int x)

{

if(x==father[x])return x;

return father[x]=find(father[x]);

}

void dfs(int k,int s,int t)

{

for(int i=head[k];i;i=next[i])

{

if(finish==1)return;

int u=point[i];

dfs(u,s,t);

int x=find(k),y=find(u);

if(x!=y)father[y]=x;

}

visit[k]=1;

if(k==s && visit[t]){printf("%d\n",find(t));finish=1;}

else if(k==t && visit[s]){printf("%d\n",find(s));finish=1;}

return ;

}

int main()

{

int tt,n,x,y,root,s,t;

scanf("%d",&tt);

while(tt--)

{

now=finish=0;

n=read();

for(int i=1;i<=n;i++)father[i]=i;

for(int i=1;i<n;i++)

{

x=read(),y=read();

add(x,y);

in[y]++;

}

for(int i=1;i<=n;i++)if(in[i]==0)root=i;else in[i]=0;

s=read(),t=read();

dfs(root,s,t);

int u=sizeof(int)*(n+3);

int v=sizeof(bool)*(n+3);

memset(visit,0,v);

memset(head,0,u);

}

return 0;

}

转载于:https://www.cnblogs.com/philippica/p/4155005.html

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