1101. The Earliest Moment When Everyone Become Friends

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My Solution

The Key Idea for Solving This Coding Question

C++ Code

class UnionFind {
public:
    UnionFind(int n) {
        groups = n;
        timestamp = 0;

        root.resize(n);
        rank.resize(n, 0);
        for (int i = 0; i < n; ++i) {
            root[i] = i;
        }
    }

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

    void unify(int x, int y, int time) {
        int rootX = find(x), rootY = find(y);

        if (rootX != rootY) {
            if (rank[rootX] < rank[rootY]) {
                root[rootX] = rootY;
            } else if (rank[rootY] < rank[rootX]) {
                root[rootY] = rootX;
            } else {
                root[rootY] = rootX;
                ++rank[rootX];
            }
            --groups;

            if (timestamp < time) {
                timestamp = time;
            }
        }
    }

    int getGroups() {
        return groups;
    }

    int getTimestamp() {
        return timestamp;
    }
private:
    int timestamp;
    int groups;

    vector<int> root;
    vector<int> rank;
};

class Solution {
public:
    int earliestAcq(vector<vector<int>> &logs, int n) {
        UnionFind uf(n);
        sort(logs.begin(), logs.end(), [](vector<int> &log1, vector<int> &log2){ return log1[0] < log2[0]; });

        for (auto &log : logs) {
            uf.unify(log[1], log[2], log[0]);
        }

        if (uf.getGroups() != 1) {
            return - 1;
        }
        return uf.getTimestamp();
    }
};

Time Complexity

Space Complexity

Miscellaneous