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Nearest Common Ancestors
Description
A rooted tree is a well-known data structure in computer science and engineering. An example is shown below:
For other examples, the nearest common ancestor of nodes 2 and 3 is node 10, the nearest common ancestor of nodes 6 and 13 is node 8, and the nearest common ancestor of nodes 4 and 12 is node 4. In the last example, if y is an ancestor of z, then the nearest Write a program that finds the nearest common ancestor of two distinct nodes in a tree. Input
The input consists of T test cases. The number of test cases (T) is given in the first line of the input file. Each test case starts with a line containing an integer N , the number of nodes in a tree, 2<=N<=10,000. The nodes are labeled with integers 1, 2,...,
N. Each of the next N -1 lines contains a pair of integers that represent an edge --the first integer is the parent node of the second integer. Note that a tree with N nodes has exactly N - 1 edges. The last line of each test case contains two distinct integers whose nearest common ancestor is to be computed. Output
Print exactly one line for each test case. The line should contain the integer that is the nearest common ancestor.
Sample Input 2 16 1 14 8 5 10 16 5 9 4 6 8 4 4 10 1 13 6 15 10 11 6 7 10 2 16 3 8 1 16 12 16 7 5 2 3 3 4 3 1 1 5 3 5 Sample Output 4 3 Source |
Rt,纯粹无聊写的……(其实至今为止就写过2个………("▔□▔)/)
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<functional>
using namespace std;
#define MAXN (10000+10)
#define Li (17)
int t,n,father[MAXN][Li];
int edge[MAXN],pre[MAXN],next[MAXN],size=0;
void addedge(int u,int v)
{
edge[++size]=v;
next[size]=pre[u];
pre[u]=size;
}
int queue[MAXN],deep[MAXN],bin[Li];
void bfs()
{
int head=1,tail=1;
for (int i=1;i<=n;i++)
if (!father[i][0]) {queue[1]=i;deep[i]=1;break;}
while (head<=tail)
{
int &u=queue[head];
for (int i=1;i<Li;i++)
{
father[u][i]=father[father[u][i-1]][i-1];
if (father[u][i]==0) break;
}
for (int p=pre[u];p;p=next[p])
{
int &v=edge[p];
deep[v]=deep[u]+1;
queue[++tail]=v;
}
head++;
}
}
int lca(int x,int y)
{
if (x==y) return x;
if (deep[x]<deep[y]) swap(x,y);
int t=deep[x]-deep[y];
for (int i=0;i<Li;i++)
if (bin[i]&t)
{
x=father[x][i];
}
int i=Li-1;
while (x^y)
{
while (father[x][i]==father[y][i]&&i) i--;
x=father[x][i];y=father[y][i];
}
return x;
}
int main()
{
// freopen("poj1330.in","r",stdin);
scanf("%d",&t);
for (int i=0;i<Li;i++) bin[i]=1<<i;
while (scanf("%d",&n)!=EOF)
{
memset(pre,0,sizeof(pre));size=0;
memset(father,0,sizeof(father));
for (int i=1;i<n;i++)
{
int u,v;
scanf("%d%d",&u,&v);
father[v][0]=u;
addedge(u,v);
}
bfs();
int x,y;
scanf("%d%d",&x,&y);
printf("%dn",lca(x,y));
}
return 0;
}
这下小