leetcode

0 class Solution {

1 public:

2 int minReorder(int n, vector<vector<int>> &connections) {

3 unordered_set<string> us;

4 vector<bool> visited(n, false);

5 vector<vector<int>> adj(n, vector<int>());

6

7 for (auto &e : connections) {

8 us.insert(to_string(e[0]) + " " + to_string(e[1]));

9 adj[e[0]].push_back(e[1]);

10 adj[e[1]].push_back(e[0]);

11 }

12

13 int res = 0;

14

15 stack<int> st;

16 st.push(0);

17 visited[0] = true;

18 while (!st.empty()) {

19 int root = st.top();

20 st.pop();

21 for (auto c : adj[root])

22 if (!visited[c]) {

23 if (!us.count(to_string(c) + " " + to_string(root))) res++;

24 visited[c] = true;

25 st.push(c);

26 }

27 }

28 return res;

29 }

30 };