HDU 1213 How Many Tables 并查集入门

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How Many Tables

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

Total Submission(s): 9407    Accepted Submission(s): 4649
[/b]

[align=left]Problem Description[/align]
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.

 

 
[align=left]Input[/align]
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.

 

 
[align=left]Output[/align]
For each test case, just output how many tables Ignatius needs at least. Do NOT print any blanks.

 

 
[align=left]Sample Input[/align]

2
5 3
1 2
2 3
4 5

5 1
2 5

 

 
[align=left]Sample Output[/align]

2
4

 

 
[align=left]Author[/align]
Ignatius.L
 

 
[align=left]Source[/align]
杭电ACM省赛集训队选拔赛之热身赛
 

 
[align=left]Recommend[/align]
Eddy
 
题意是说Ignatius请朋友吃饭，认识的坐在一起，如果A认识B，B认识C，那么A认识C。让你求最少需要多少张桌子。

#include<stdio.h>
int num[1007],pre[1007];
int n,m;
void init()
{
for(int i=1;i<1007;i++)
{
num[i]=1;
pre[i]=i;
}
}

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

void unio(int x,int y)
{
int a,b;
a=find(x);
b=find(y);
if(a==b)return;
pre[a]=b;
}
int main()
{
int t;
scanf("%d",&t);
while(t--)
{
init();
scanf("%d%d",&n,&m);
int a,b;
while(m--)
{
scanf("%d%d",&a,&b);
unio(a,b);
}
int ans=0;
for(int i=1;i<=n;i++)
if(pre[i]==i)
ans++;
printf("%d\n",ans);
}
return 0;
}