poj1330 Nearest Common Ancestors

来源：互联网发布：佳能小型打印机软件编辑：程序博客网时间：2024/05/08 05:12

题目链接：..G20过了再补

题目大意：求最近公共祖先...水..

题解：倍增LCA/树剖

就是练模版的题...话说看了一下，我的树剖比倍增还快了那么一丢丢..

注意：不是无根树啊233

#include<cstdio>#include<cstring>#include<iostream>#include<cstdlib>#include<iostream>#include<algorithm>using namespace std;#define maxn 20100struct node{int x,y,next;}a[maxn];int len,first[maxn];void ins(int x,int y){len++;a[len].x=x;a[len].y=y;a[len].next=first[x];first[x]=len;}int fa[maxn],son[maxn],dep[maxn];int tot[maxn],top[maxn];void dfs1(int x){son[x]=0;tot[x]=1;for (int k=first[x];k!=-1;k=a[k].next){int y=a[k].y;if (y!=fa[x]){fa[y]=x;dep[y]=dep[x]+1;dfs1(y);if (tot[son[x]]<tot[y]) son[x]=y;tot[x]+=tot[y];}}}void dfs2(int x,int tp){top[x]=tp;if (son[x]!=0) dfs2(son[x],tp);for (int k=first[x];k!=-1;k=a[k].next){int y=a[k].y;if (y!=fa[x] && y!=son[x]) dfs2(y,y);}}int lca(int x,int y){int ty=top[y],tx=top[x];while (tx!=ty){if (dep[tx]>dep[ty]){int tt=tx;tx=ty;ty=tt;tt=x;x=y;y=tt;}y=fa[ty];ty=top[y];}if (x==y) return x;else{if (dep[x]>dep[y]){int tt=x;x=y;y=tt;}return x;}}int main(){//freopen("a.in","r",stdin);//freopen("a.out","w",stdout);int T,n,x,y,i,rt;scanf("%d",&T);while (T--){len=0;memset(first,-1,sizeof(first));scanf("%d",&n);rt=(1+n)*n/2;for (i=1;i<n;i++){scanf("%d%d",&x,&y);ins(x,y);ins(y,x);rt-=y;}fa[rt]=0;dep[rt]=0;dfs1(rt);dfs2(rt,rt);scanf("%d%d",&x,&y);printf("%d\n",lca(x,y));}return 0;}

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