HDU 1856 More is better （並查集）

More is better

Time Limit: 5000/1000 MS (Java/Others) Memory Limit: 327680/102400 K (Java/Others)
Total Submission(s): 15639 Accepted Submission(s): 5761


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

4
1 2
3 4
5 6
1 6
4
1 2
3 4
5 6
7 8

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.
  

這也是一個並查序的問題，問的是friends最多有多少個，其實就是計算ranks的最大值。

#include
#include
using namespace std;
#define M 10000010
int ranks[M];//一開始還以為空間不夠，結果這題給的空間很大
int pre[M];
int _find(int node)
{
    int t=node;
    if(node==pre[node])return node;
    else
        return pre[node]=_find(pre[node]);
}
int _union(int a,int b)
{
    int p=_find(a);
    int q=_find(b);
    if(p!=q)
    {
        if(ranks[p]max)max=ranks[i];
        }
        printf("%d\n",max);

    }
    return 0;
}