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好路径的数目⚓︎

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<int> maxCnt;

    void build(int n) {
        p.resize(n);
        maxCnt.resize(n);

        for (int i = 0; i < n; i++) {
            p[i] = i;
            maxCnt[i] = 1;
        }
    }

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

    int unionSets(int x, int y, vector<int>& vals) {
        int fx = find(x), fy = find(y);
        int path = 0;
        if (vals[fx] > vals[fy]) {
            p[fy] = fx;
        } else if (vals[fx] < vals[fy]) {
            p[fx] = fy;
        } else {
            path = maxCnt[fx] * maxCnt[fy];
            p[fy] = fx;
            maxCnt[fx] += maxCnt[fy];
        }
        return path;
    }

public:
    int numberOfGoodPaths(vector<int>& vals, vector<vector<int>>& edges) {
        int n = vals.size();
        build(n);
        int res = n;

        sort(edges.begin(), edges.end(), [&](auto& lhs, auto& rhs) {
            return max(vals[lhs[0]], vals[lhs[1]]) < max(vals[rhs[0]], vals[rhs[1]]);
        });

        for (auto edge : edges) {
            res += unionSets(edge[0], edge[1], vals);
        }
        return res;
    }
};