leetcode/algorithms/cpp/redundantConnectionII/redundantConnectionII.cpp at main · MichelleZ/leetcode · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
// Source: https://leetcode.com/problems/redundant-connection-ii/
// Author: Miao Zhang
// Date:   2021-03-01

class Solution {
public:
    vector<int> findRedundantDirectedConnection(vector<vector<int>>& edges) {
        vector<int> parents(edges.size() + 1, 0);
        vector<int> roots(edges.size() + 1, 0);
        vector<int> sizes(edges.size() + 1, 1);

        vector<int> ans1;
        vector<int> ans2;

        for (auto& edge: edges) {
            int u = edge[0];
            int v = edge[1];
            if (parents[v] > 0) {
                ans1 = {parents[v], v};
                ans2 = edge;

                edge[0], edge[1] = -1;
            }
            parents[v] = u;
        }

        for (const auto& edge: edges) {
            int u = edge[0];
            int v = edge[1];
            if (u < 0 || v < 0) continue;
            if (!roots[u]) roots[u] = u;
            if (!roots[v]) roots[v] = v;
            int pu = find(u, roots);
            int pv = find(v, roots);
            if (pu == pv) {
                return ans1.empty() ? edge: ans1;
            }
            if (sizes[pv] > sizes[pu]) swap(pu, pv);
            roots[pv] = pu;
            sizes[pu] += sizes[pv];
        }
        return ans2;
    }

private:
    int find(int node, vector<int>& roots) {
        while (roots[node] != node) {
            roots[node] = roots[roots[node]];
            node = roots[node];
        }
        return node;
    }
};