暢通工程 -HDU - 1863

題意：Kruskal算法最小生成樹

AC代碼：

#include <iostream>
using namespace std;
const int maxn1 = 1005;
int par[maxn1];
int rank1[maxn1];

void init() {
    for (int i = 0; i <= maxn1; i++) {
        par[i] = i;
        rank1[i] = 0;
    }
}

int Find(int x) {
    if (par[x] == x)
        return x;
    else
        return par[x] = Find(par[x]);
}

void unite(int x, int y) {
    x = Find(x);
    y = Find(y);
    if (x == y)
        return;
    if (rank1[x] < rank1[y])
        par[x] = y;
    else {
        par[y] = x;
        if (rank1[x] == rank1[y])
            rank1[x]++;
    }
}


bool same(int x, int y) {
    return Find(x) == Find(y);
}

int main() {
    int m, n;
    while (cin >> n) {
        if (n == 0)
            break;
        cin >> m;
        init();
        while (m--) {
            int a[2];
            scanf("%d %d", &a[0], &a[1]);
            unite(a[0], a[1]);
        }
        int ans = 0;
        for (int i = 1; i < n; ++i) {
            for (int j = i + 1; j <= n; ++j) {
                if (!same(i, j)) {
                    ans++;
                    unite(i,j);
                }
            }
        }
        cout<<ans<<endl;
    }
    return 0;
}