题目链接

食物链 POJ - 1182

思路

$$ \begin{aligned}并查集经典入门题\end{aligned} $$

时间复杂度

$$ O(N \alpha (N)) $$

代码

#include <cstdio>
#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);
    }
};


int main() {
    int n, k;
    scanf("%d%d", &n, &k);// don't forget &
    DSU dsu;
    dsu.init(3 * n);
    int ans = 0;
    while (k--) {
        int d, x, y;
        scanf("%d%d%d", &d, &x, &y);// don't forget &
        if (x > n || y > n) {
            ans++;
            continue;
        }
        if (d == 1) {
            if (dsu.same(x, y + n) || dsu.same(x, y + 2 * n)) {
                ans++;
            } else {
                dsu.unite(x, y);
                dsu.unite(x + n, y + n);
                dsu.unite(x + 2 * n, y + 2 * n);
            }
        } else {
            if (x == y) {
                ans++;
                continue;
            }
            if (dsu.same(x, y) || dsu.same(x, y + 2 * n)) {
                ans++;
            } else {
                dsu.unite(x, y + n);
                dsu.unite(x + n, y + 2 * n);
                dsu.unite(x + 2 * n, y);
            }
        }
    }
    printf("%d", ans);

    return 0;
}