leetcode

0 class Solution {

1 public:

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

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

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

5 stack<int> st;

6 int res = 0;

7

8 for (auto &e : connections) {

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

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

11 }

12

13 st.push(0);

14 visited[0] = true;

15 while (!st.empty()) {

16 int root = st.top();

17 st.pop();

18 for (auto c : adj[root]) {

19 int ac = abs(c);

20 if (!visited[ac]) {

21 res += c > 0;

22 visited[ac] = true;

23 st.push(ac);

24 }

25 }

26 }

27 return res;

28 }

29 };