题目链接

Bad Cowtractors POJ - 2377

思路

$$ 最大生成树模板题\\\\注意判断连通性！ $$

时间复杂度

$$ O((M)log(M)) $$

代码

#include <cstdio>
#include <algorithm>
#include <vector>

using namespace std;

class DSU {
public:
    vector<int> p, r;

    void init(int n) {
        p.resize(n + 10);
        r.resize(n + 10);
        for (int i = 0; i <= n; i++) {
            p[i] = i;
            r[i] = 0;
        }
    }

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

    bool unite(int x, int y) {
        x = find(x);
        y = find(y);
        if (x == y) {
            return false;
        }

        if (r[x] < r[y]) {
            p[x] = y;
        } else {
            p[y] = x;
            if (r[x] == r[y]) {
                r[x]++;
            }
        }
        return true;
    }

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

DSU dsu;
int n, m;
const int MAXN = 2e4 + 10;
int a[MAXN], b[MAXN], c[MAXN], id[MAXN];

bool cmp(int x, int y) {
    return c[x] > c[y];
}

int main() {
    scanf("%d%d", &n, &m);// don't forget &
    dsu.init(n);
    for (int i = 1; i <= m; i++) {
        scanf("%d%d%d", &a[i], &b[i], &c[i]);// don't forget &
        id[i] = i;
    }
    sort(id + 1, id + 1 + m, cmp);
    long long ans = 0;
    for (int i = 1; i <= m; i++) {
        int x = id[i];
        if (!dsu.same(a[x], b[x])) {
            ans += c[x];
            dsu.unite(a[x], b[x]);
        }
    }
    int w = dsu.find(1);
    for (int i = 1; i <= n; i++) {
        if (w != dsu.find(i)) {
            ans = -1;
            break;
        }
    }
    printf("%lld", ans);
    return 0;
}