Leetcode #94 Inorder Traversal of Binary Tree

inorderTraversal.cpp

class Solution {
public:
    vector<int> inorderTraversal(TreeNode* root) {
        vector<int> inorder;
        stack<TreeNode*> nodes;
        
        if(root == NULL) return inorder;
        
        while(root != NULL || !nodes.empty()){
            //push left children if available
            while(root != NULL){
                nodes.push(root);
                root = root->left;
            }
            
            //retrieve top node and store its right child if exists
            root = nodes.top();
            nodes.pop();
            
            inorder.push_back(root->val);
            root = root->right;
        }
        
        return inorder;
    }
};