HDU - 1213 How Many Tables 【并查集】

题目链接

http://acm.hdu.edu.cn/showproblem.php?pid=1213

题意
给出N个人 M对关系 找出共有几对连通块

思路
并查集

AC代码

#include <cstdio>
#include <cstring>
#include <ctype.h>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <ctime>
#include <iostream>
#include <algorithm>
#include <deque>
#include <vector>
#include <queue>
#include <string>
#include <map>
#include <stack>
#include <set>
#include <numeric>
#include <sstream>
#include <iomanip>
#include <limits>

#define CLR(a, b) memset(a, (b), sizeof(a))
#define pb push_back

using namespace std;
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef pair <int, int> pii;
typedef pair <ll, ll> pll;
typedef pair<string, int> psi;
typedef pair<string, string> pss;

const double PI = acos(-1.0);
const double E = exp(1.0);
const double eps = 1e-30;

const int INF = 0x3f3f3f3f;
const int maxn = 5e4 + 10;
const int MOD = 1e9 + 7;

int pre[maxn];

int find(int x)
{
    int r = x;
    while (pre[r] != r)
        r = pre[r];
    int i = x, j;
    while (i != r)
    {
        j = pre[i];
        pre[i] = r;
        i = j;
    }
    return r;
}

void join(int x, int y)
{
    int fx = find(x), fy = find(y);
    if (x != fy)
        pre[fx] = fy;
}

void init()
{
    for (int i = 0; i < maxn; i++)
        pre[i] = i;
}

int main()
{
    int t;
    cin >> t;
    while (t--)
    {
        init();
        int n, m;
        scanf("%d%d", &n, &m);
        int x, y;
        for (int i = 0; i < m; i++)
        {
            scanf("%d%d", &x, &y);
            join(x, y);
        }
        map <int, int> M;
        for (int i = 1; i <= n; i++)
            M[find(i)]++;
        cout << M.size() << endl;
    }
}