题目链接

Find them, Catch them POJ - 1703

思路

$$ \begin{aligned}并查集基础题。\end{aligned} $$

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 T;
    scanf("%d", &T);// don't forget &
    DSU dsu;
    char op[5];
    while (T--) {
        int n, m;
        scanf("%d%d", &n, &m);// don't forget &
        dsu.init(2 * n);
        while (m--) {
            int x, y;
            scanf("%s%d%d", op, &x, &y);
            if (x > y) {
                swap(x, y);
            }
            if (op[0] == 'D') {
                dsu.unite(x, y + n);
                dsu.unite(x + n, y);
            } else {
                if (dsu.same(x, y)) {
                    puts("In the same gang.");
                } else if (dsu.same(x, y + n)) {
                    puts("In different gangs.");
                } else {
                    puts("Not sure yet.");
                }
            }
        }
    }
    return 0;
}