HDU：1213 How Many Tables（简单并查集）

How Many Tables

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)

Total Submission(s): 24376    Accepted Submission(s): 12201


Problem Description

Today is Ignatius' birthday. He invites a lot of friends. Now it's dinner time. Ignatius wants to know how many tables he needs at least. You have to notice that not all the friends know each other, and all the friends do not want to stay with strangers.

One important rule for this problem is that if I tell you A knows B, and B knows C, that means A, B, C know each other, so they can stay in one table.

For example: If I tell you A knows B, B knows C, and D knows E, so A, B, C can stay in one table, and D, E have to stay in the other one. So Ignatius needs 2 tables at least.

 

Input

The input starts with an integer T(1<=T<=25) which indicate the number of test cases. Then T test cases follow. Each test case starts with two integers N and M(1<=N,M<=1000). N indicates the number of friends, the friends are marked from 1 to N. Then M lines
follow. Each line consists of two integers A and B(A!=B), that means friend A and friend B know each other. There will be a blank line between two cases.

 

Output

For each test case, just output how many tables Ignatius needs at least. Do NOT print any blanks.

 

Sample Input

2
5 3
1 2
2 3
4 5

5 1
2 5

 

Sample Output

2
4

 

Author

Ignatius.L

 

Source

杭电ACM省赛集训队选拔赛之热身赛

 

Recommend

Eddy

题目大意：一个人办聚会，要来的人不是朋友的不能坐一桌，坐一桌的朋友可以是间接的朋友。问最少需要准备多少张桌子。

解题思路：并查集连接后，求树的个数。

代码如下：

#include <cstdio>
int pre[1010];
int find(int x)
{
int r=x;
while(r!=pre[r])
{
r=pre[r];
}
return r;
}
int main()
{
int t;
scanf("%d",&t);
while(t--)
{
int n ,m;
scanf("%d%d",&n,&m);
for(int i=1;i<=n;i++)//初始化
{
pre[i]=i;
}
for(int i=0;i<m;i++)
{
int x,y;
scanf("%d%d",&x,&y);
int fx=find(x);
int fy=find(y);
if(fx!=fy)
{
pre[fx]=fy;
}
}
int cnt=0;
for(int i=1;i<=n;i++)//求树的个数
{
if(pre[i]==i)
{
cnt++;
}
}
printf("%d\n",cnt);
}
return 0;
}