HDU 1856 More is better （并查集基本操作）

末蓝、 2022-06-13 13:58 78阅读 0赞

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.

题解：

本来是不想写这题的题解的，因为太水了，但是居然tle了几次。。后来发现手抖打错了点东西。。下不为例

代码：

#include<stdio.h>
    #include<cstring>
    #include<string>
    #include<iostream>
    #include<algorithm>
    #include<math.h>
    #include<queue>
    #include<stack>
    #include<map>
    using namespace std;
    const int MAX=1e7+5;
    int pre[MAX];
    int mul[MAX];
    int find(int x)
    {
        if(x!=pre[x])
            pre[x]=find(pre[x]);//注意点,缩小树的深度以节省时间
        return pre[x];
    }
    int main()
    {
        int i,j,n,x,y,d1,d2,maxx,max=MAX-5;
        while(scanf("%d",&n)!=EOF)
        {
            if(n==0)
            {
                printf("1\n");
                continue;
            }
            maxx=1;
            for(i=1;i<=max;i++)
            {
                pre[i]=i;
                mul[i]=1;
            }
            max=0;
            for(i=1;i<=n;i++)
            {
                scanf("%d%d",&x,&y);
                if(x>y)
                    swap(x,y);
                if(y>max)
                    max=y;
                d1=find(x);
                d2=find(y);
                if(d1!=d2)
                {
                    mul[d1]+=mul[d2];
                    pre[d2]=d1;
                    if(mul[d1]>maxx)
                        maxx=mul[d1];
                }
            }
            printf("%d\n",maxx);
        }
        return 0;
    }