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POJ1308-并查集

2013年04月29日 ⁄ 综合 ⁄ 共 1474字 ⁄ 字号 评论关闭

题目:题目链接

 

题意:给出你每对点的链接情况,问你最后构成的是不是一棵树

 

分析:并查集,判断是不是有多个根即可(按照树 的定义,只有一个根。每个子节点只能有一个父节点)。对了,没

有节点也算树,就是说空树也算:

 

代码:

#include <iostream>
#include <cstdio>
#include <string>
#include <string.h>
#include <map>
#include <vector>
#include <cstdlib>
#include <algorithm>
#include <cmath>
#include <queue>
#include <set>
#include <stack>
#include <functional>
#include <fstream>
#include <sstream>
#include <iomanip>
#include <numeric>
#include <cassert>
#include <bitset>
#include <stack>
#include <ctime>
#include <list>
#define INF 0x7fffffff
#define max3(a,b,c) (max(a,b)>c?max(a,b):c)
#define min3(a,b,c) (min(a,b)<c?min(a,b):c)
#define mem(a,b) memset(a,b,sizeof(a))
using namespace std;

int QuickMod(int  a,int b,int n)
{
    int r = 1;
    while(b)
    {
        if(b&1)
            r = (r*a)%n;
        a = (a*a)%n;
        b >>= 1;
    }
    return r;
}
#define N 10005
int father[N],vis[N];
int find(int x)
{
    int r = x;
    while(father[r] != r)
        r = father[r];
    return r;
}
void merge(int fx,int fy)
{
    if (fx < fy)
        father[fx] = fy;
    else
        father[fy] = fx;
}
int main()
{
    int n, m;
    int cnt = 1;
    int flag;
    int max = -1;
    int fa,fb;
    while(cin >> n >>m)
    {
        if(n == -1&&m == -1)
            return 0;
        if(n==0 && m==0)
        {
            cout<<"Case "<<cnt++<<" is a tree."<<endl;
            continue;
        }
        flag = 0;
        for(int i = 1; i <= N; i++)
        {
            father[i] = i;
            vis[i] = 0;
        }
        if(n > max)
            max=n;
        if(m > max)
            max = m;
        vis[n] = vis[m]=1;
        fa = find(n);
        fb = find(m);
        if(fa == fb)
            flag++;
        else
            merge(fa, fb);
        while(cin >> n >> m)
        {
            if(n == 0&& m == 0)
                break;
            if(n > max)
                max=n;
            if(m > max)
                max=m;
            fa = find(n);
            fb = find(m);
            vis[n] = vis[m] = 1;
            if(fa == fb)
                flag++;
            else
                merge(fa, fb);
        }
        for( int i = 1; i <= max; i++ )
            if(vis[i] && father[i] == i )
            {
                flag++;
            }
        if(flag==1)
            cout<<"Case "<<cnt++<<" is a tree."<<endl;
        else
            cout<<"Case "<<cnt++<<" is not a tree."<<endl;

    }
    return 0;
}

 

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