HDU - 1213 - How Many Tables

梦里梦外; 2022-06-10 00:09 147阅读 0赞

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题目连接：[http://acm.hdu.edu.cn/showproblem.php?pid=1213][http_acm.hdu.edu.cn_showproblem.php_pid_1213]

## 题目描述 ##

### 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

## 解题思路 ##

题意：一共n个节点，给m条边，问是否能后全部连起来。  
思路：用并查集吧边输入进去，然后查找根节点有几个即可，即 pre\[i\] = i 的个数  
[并查集详细介绍][Link 1]

## AC代码 ##

#include<iostream>
    #include<cstring>
    #define N 1010
    using namespace std;
    int pre[N];
    int find(int x) {
        return x == pre[x] ? x : find(pre[x]);
    }
    void join(int a, int b) {
        int x = find(a);
        int y = find(b);
        pre[x] = y;
    }
    int main () {
        int t;
        scanf("%d", &t);
        while(t--) {
            int n, m;
            scanf("%d %d", &n, &m);
            for(int i = 1; i <= n; i++) 
                pre[i] = i;
            for(int i = 1; i <= m; i++) {
                int a, b;
                scanf("%d %d", &a, &b);
                join(a, b);
            }
            int ans = 0;
            for(int i = 1; i <= n; i++) 
                if(pre[i] == i) 
                    ans++; 
            printf("%d\n", ans);
        } 
        return 0;
    }

[http_acm.hdu.edu.cn_showproblem.php_pid_1213]: http://acm.hdu.edu.cn/showproblem.php?pid=1213
[Link 1]: http://blog.csdn.net/xiao_bai_9527/article/details/76730366