algorithms

Algorithm implementations
git clone git://git.laack.co/algorithms.git
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preorder-traversal-iterative.cpp (1082B)

      1 /**
      2  * Definition for a binary tree node.
      3  * struct TreeNode {
      4  *     int val;
      5  *     TreeNode *left;
      6  *     TreeNode *right;
      7  *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
      8  *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
      9  *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
     10  * };
     11  */
     12 class Solution {
     13 public:
     14     vector<int> preorderTraversal(TreeNode* root) {
     15         
     16         auto nodeLs = vector<TreeNode*>{root};
     17         auto returnLs = vector<int>{};
     18         
     19         while (nodeLs.size() > size_t(0)) {
     20             auto* current = nodeLs.back();
     21             nodeLs.pop_back();
     22             
     23             if(current == nullptr) {
     24                 continue;
     25             }
     26 
     27             returnLs.push_back(current->val);
     28 
     29             // preorder so we add current then traverse left
     30             // then traverse right. (NOTE: Remember this is stack so last item is popped)
     31 
     32             nodeLs.push_back(current->right);
     33             nodeLs.push_back(current->left);
     34         }
     35 
     36         return returnLs;
     37     }
     38 };