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And lookup template

Learned from lc user "Code Caprice".

	int n; // 并查集边的数量
    vector<int> father;  //在函数里使用father.resize(n)

    // 并查集初始化
    void init() {
    
    
        for (int i = 0; i < n; ++i) {
    
    
            father[i] = i;
        }
    }
    // 并查集里寻根的过程
    int find(int u) {
    
    
        return u == father[u] ? u : father[u] = find(father[u]);
    }
    // 将v->u 这条边加入并查集
    void join(int u, int v) {
    
    
        u = find(u);
        v = find(v);
        if (u == v) return ;
        father[v] = u;
    }
    // 判断 u 和 v是否找到同一个根
    bool same(int u, int v) {
    
    
        u = find(u);
        v = find(v);
        return u == v;
    }

lc topic:

547. The number of provinces – simple union search
721. Account merger – use union search to merge data
1584. The minimum cost of linking all points – use union search to assist judgment