【并查集】hdu 1325 Is It A Tree? 或 poj 1308 Is It A Tree?

/* THE PROGRAM IS MADE BY PYY */
/*----------------------------------------------------------------------------//
    Copyright (c) 2012 panyanyany All rights reserved.

    URL   : http://acm.hdu.edu.cn/showproblem.php?pid=1325
    Name  : 1325 Is It A Tree?

    Date  : Tuesday, April 10, 2012
    Time Stage : one hour

    Result:
5744703	2012-04-10 16:19:24	Accepted	1325
0MS	612K	1133 B
C++	pyy


Test Data :

Review :
hdu 的数据比poj弱，没有以下两种情况：
0 0
1 1 0 0
答案都是 not a tree。
除此之外要注意的是循环的情况：
1 2 1 3 2 1 0 0 // not a tree
和两棵树的情况：
1 2 3 4 0 0 //not a tree
//----------------------------------------------------------------------------*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <vector>

#include <algorithm>
#include <iostream>
#include <queue>

using namespace std ;

#define MAXN    (1002)

int		set[MAXN];
int		flag;
int		tcase;

void init()
{
    int i;
    memset(set, -1, sizeof(set));
    flag = 0;
}

int find(int x)
{
    if (set[x] == -1)
        set[x] = x;
    if (set[x] == x)
        return x;
    return set[x] = find(set[x]);
}

int main()
{
    int i, j;
    int x, y;
    tcase = 1;
    init();
    while (scanf("%d %d", &x, &y) != EOF)
    {
        if (x == -1 && y == -1)
            break;
        if (x == 0 && y == 0)
        {
            printf ("Case %d", tcase++);
            if (!flag)
            {
                j = 0;
                for (i = 0; i < MAXN; ++i)
                    if (set[i] == i)
                        ++j;
					if (j > 1)    // not a tree: 1 2 3 4 0 0, a tree: 0 0
						flag = 1;
            }
            if (!flag)
            {
                printf (" is a tree.\n");
            }
            else
                printf (" is not a tree.\n");
            init();
            continue;
        }
        int px = find(x);
        int py = find(y);
		
        if (py != y && px != py || x == y || (x != y && px == py))// not a tree: 1 2 1 3 2 1 0 0
        {// not a tree: 1 1 0 0
            flag = 1;
        }
        else
            set[py] = set[px];
    }
    return 0;
}