hdu1232 畅通工程--并查集

#define _CRT_SECURE_NO_DEPRECATE

#include<iostream>
#include<cmath>
#include<algorithm>

using namespace std;

int father[1005];
int n, m;
int a, b;

int find(int x)
{
return x == father[x] ? x : find(father[x]);
}

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

int main()
{
while (~scanf("%d", &n) && n)
{
scanf("%d", &m);
if (m == 0)
printf("%d\n", n - 1);
else
{
for (int i = 1; i <= n; i++)
father[i] = i;

for (int i = 1; i <= m; i++)
{
scanf("%d%d", &a, &b);
join(a, b);
}

int ans = 0;
for (int i = 1; i <= n; i++)
{
if (i == find(i))
ans++;
}

printf("%d\n", ans - 1);
}
}
return 0;
}