leetcode 261 以图判树

leetcode 261 以图判树

题目

并查集

模板

class UF {
public:
    UF(int size) {
        father.resize(size);
        for (int i = 0; i < size; ++i) {
            father[i] = i;
        }
    }
    int find (int x) {
        return x == father[x] ? x : father[x] = find(father[x]);
    }
    void connect (int x, int y) {
        int xx = find(x);
        int yy = find(y);
        if (xx == yy) { return; }
        if (xx < yy) {
            father[yy] = xx;
        } else {
            father[xx] = yy;
        }
    }
    bool same(int x, int y) {
        return find(x) == find(y);
    }
private:
    vector<int> father;
};

代码

class Solution {
public:
    bool validTree(int n, vector<vector<int>>& edges) {
        UF uf(n);
        if (edges.size() != n-1) {
            return false;
        }
        for (auto& e : edges) {
            int v1 = e[0], v2 = e[1];
            int v1_par = uf.find(v1);
            int v2_par = uf.find(v2);
            if (v1_par == v2_par) {
                return false;
            }
            uf.connect(v1, v2);
        }
        return true;
    }
};