HDU-1232-畅通工程

ACM模版

描述

题解

经典的并查集问题，最后查看有多少根，结果为根数-1。

代码

#include 
#include 
#include 

#define mem(a, b) memset(a, b, sizeof(a))

using namespace std;

const int MAXN = 1010;

int maxRoom;
int pre[MAXN];
int root;

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

    return ;
}

int main(int argc, const char * argv[])
{
    int N, M;
    int A, B;
    while (~scanf("%d", &N) && N != 0)
    {
        scanf("%d", &M);

        for (int i = 0; i <= MAXN; i++)
        {
            pre[i] = i;
        }

        for (int i = 0; i < M; i++)
        {
            scanf("%d%d", &A, &B);
            join(A, B);
        }

        root = 0;
        for (int i = 1; i <= N; i++)
        {
            if (pre[i] == i)
            {
                root++;
            }
        }

        cout << root - 1 << '\n';
    }

    return 0;
}