message: Update time-needed-to-inform-all-employees.cpp
diff: // Time: O(n)
  // Space: O(n)
  +// dfs solution with stack
  class Solution {
  +public:
  + int numOfMinutes(int n, int headID, vector<int>& manager, vector<int>& informTime) {
  + unordered_map<int, vector<int>> children;
  + for (int i = 0; i < manager.size(); ++i) {
  + if (manager[i] != -1) {
  + children[manager[i]].emplace_back(i);
  + }
  + }
  +
  + int result = 0;
  + vector<pair<int, int>> stk = {{headID, 0}};
  + while (!stk.empty()) {
  + auto [node, curr] = stk.back(); stk.pop_back();
  + curr += informTime[node];
  + result = max(result, curr);
  + if (!children.count(node)) {
  + continue;
  + }
  + for (const auto& child : children.at(node)) {
  + stk.emplace_back(child, curr);
  + }
  + }
  + return result;
  + }
  +};
  +
  +// Time: O(n)
  +// Space: O(n)
  +// dfs solution with recursion
  +class Solution2 {
  public:
  int numOfMinutes(int n, int headID, vector<int>& manager, vector<int>& informTime) {
  unordered_map<int, vector<int>> children;
  