hdu 1213 How Many Tables(并查集)

How Many Tables

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 16006    Accepted Submission(s): 7883

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

25 31 22 34 55 12 5

 

Sample Output

24

 

Author

Ignatius.L

 

Source

杭电ACM省赛集训队选拔赛之热身赛

 

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因为初始化par[i]=i,所以最后只要判断每个节点的父节点是不是自己就可以了，是的话ans++;

#include<cstdio>#include<iostream>#include<algorithm>#define N 1010using namespace std;int n,m;int par[N],R[N];void init() {    for(int i=0; i<=n; i++) {        par[i]=i;        R[i]=0;    }}int Find(int x) {    if(par[x]==x)return x;    return par[x]=Find(par[x]);}void unite(int x,int y) {    x=Find(x);    y=Find(y);    if(x==y)return;    if(R[x]<R[y])par[x]=y;    else  {        par[y]=x;        if(R[x]==R[y])            R[x]++;    }}bool same(int x,int y) {    return Find(x)==Find(y);}int main() {    int t;    cin>>t;    while(t--) {        scanf("%d%d",&n,&m);        int x,y;        init();        while(m--) {            scanf("%d%d",&x,&y);            unite(x,y);        }        int ans=0;        for(int i=1; i<=n; i++)            if(par[i]==i)ans++;        cout<<ans<<endl;    }}