[并查集] [HDU] 1232 畅通工程

标准并查集

求有几个独立区间

减一即可

#include <iostream>
using namespace std;

const int MAXN = 1e4 + 10;

int arr[MAXN];

void init(int N)
{
    for(int i = 1; i <= N; i++)
        arr[i] = i;
}

int find(int x)
{
    if(arr[x] == x)
        return x;
    return arr[x] = find(arr[x]);
}

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

int cal(int N)
{
    int ans = 0;

    for(int i = 1; i <= N; i++)
        if(find(i) == i)
            ans ++;

    return ans;
}

int main()
{
    ios::sync_with_stdio(false);

    int N, M, x, y;

    while(cin>>N && N)
    {
        init(N);

        cin>>M;

        while(M--)
        {
            cin>>x>>y;

            join(x, y);
        }

        cout<<cal(N) - 1<<endl;
    }
    return 0;
}