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找出知晓秘密的所有专家⚓︎

Leetcode题目链接

描述⚓︎

详见中文题目链接。

解答⚓︎

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class Solution {
private:
    vector<int> p;
    vector<bool> secret;

    void build(int n, int firstPerson) {
        p.resize(n);
        secret.resize(n);
        for (int i = 0; i < n; i++) {
            p[i] = i;
            secret[i] = false;
        }

        p[firstPerson] = 0;
        secret[0] = true;
    }

    int find(int i) {
        if (i != p[i]) p[i] = find(p[i]);
        return p[i];
    }

    void unionSets(int x, int y) {
        int fx = find(x), fy = find(y);
        if (fx != fy) {
            p[fx] = fy;
            secret[fy] = secret[fx] || secret[fy];
        }
    }

public:
    vector<int> findAllPeople(int n, vector<vector<int>>& meetings, int firstPerson) {
        build(n, firstPerson);
        sort(meetings.begin(), meetings.end(), [](auto& lhs, auto& rhs) { 
            return lhs[2] < rhs[2]; 
        });

        int m = meetings.size();
        for (int l = 0, r; l < m; ) {
            r = l;
            while (r + 1 < m && meetings[l][2] == meetings[r + 1][2]) {
                r++;
            }

            for (int i = l; i <= r; i++) {
                unionSets(meetings[i][0], meetings[i][1]);
            }

            for (int i = l, a, b; i <= r; i++) {
                a = meetings[i][0]; b = meetings[i][1];
                // reset
                if (!secret[find(a)]) p[a] = a;
                if (!secret[find(b)]) p[b] = b;
            }

            l = r + 1;
        }

        vector<int> res;
        for (int i = 0; i < n; i++) {
            if (secret[find(i)]) res.emplace_back(i);
        }
        return res;
    }
};