LeetCode589. N叉树的前序遍历

题目

法一、递归

class Solution {
public:
    vector<int>ans;
    void dfs(Node* root){
        if(root!=NULL){
            ans.push_back(root->val);
            for(int i = 0;i < root->children.size();i++)
            preorder(root->children[i]);
        }
    }
    vector<int> preorder(Node* root) {
        dfs(root);
        return ans;
    }
};

法二，用栈迭代

class Solution {
public:
    vector<int> preorder(Node* root) {
      vector<int>ans;
      stack<Node*>v;
      if(root==NULL) return ans;
      v.push(root);
      while(!v.empty()){
          Node *node = v.top();v.pop();
          if(node) ans.push_back(node->val);
          else continue;

          for(int i = node->children.size()-1;i >= 0;i--){
              v.push(node->children[i]);
          }
      }
      return ans;
    }
};