HDU1856：More is better（并查集）

最新推荐文章于 2019-06-29 14:23:40 发布

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本文介绍了一个关于并查集的应用问题——如何通过一系列已知的朋友关系找出最大可能被保留的人数。通过具体示例和代码实现，展示了并查集算法在解决此类问题中的应用。

More is better

Time Limit: 5000/1000 MS (Java/Others) Memory Limit: 327680/102400 K (Java/Others)
Total Submission(s): 25930 Accepted Submission(s): 9308

Problem Description

Mr Wang wants some boys to help him with a project. Because the project is rather complex, the more boys come, the better it will be. Of course there are certain requirements.

Mr Wang selected a room big enough to hold the boys. The boy who are not been chosen has to leave the room immediately. There are 10000000 boys in the room numbered from 1 to 10000000 at the very beginning. After Mr Wang's selection any two of them who are still in this room should be friends (direct or indirect), or there is only one boy left. Given all the direct friend-pairs, you should decide the best way.

Input

The first line of the input contains an integer n (0 ≤ n ≤ 100 000) - the number of direct friend-pairs. The following n lines each contains a pair of numbers A and B separated by a single space that suggests A and B are direct friends. (A ≠ B, 1 ≤ A, B ≤ 10000000)

Output

The output in one line contains exactly one integer equals to the maximum number of boys Mr Wang may keep.

Sample Input

Sample Output

  
   4
2


   
    
     Hint
    
A and B are friends(direct or indirect), B and C are friends(direct or indirect), 
then A and C are also friends(indirect).

 In the first sample {1,2,5,6} is the result.
In the second sample {1,2},{3,4},{5,6},{7,8} are four kinds of answers.

Author

lxlcrystal@TJU

Source

HDU 2007 Programming Contest - Final

并查集入门

# include <stdio.h>
# include <algorithm>
# define MAXN 10000000
using namespace std;
int pre[MAXN+1], num[MAXN+1];

void init()
{
    for(int i=1; i<=MAXN; ++i)
    {
        pre[i] = i;
        num[i] = 1;
    }
}

int find(int x)
{
    if(x != pre[x])
        pre[x] = find(pre[x]);
    return pre[x];
}

int main()
{
    int n, x, y, imax;
    while(~scanf("%d",&n))
    {
        if(n==0)
        {
            puts("1");
            continue;
        }
        init();
        imax = -1;
        while(n--)
        {
            scanf("%d%d",&x,&y);
            int px = find(x);
            int py = find(y);
            if(px != py)
            {
                pre[px] = py;
                num[py] += num[px];
                imax = max(imax, num[py]);
            }
        }
        printf("%d\n",imax);
    }
    return 0;
}