Iterative binary tree traversals

iter_tree_trav.cpp

    vector<int> inorderTraversal(TreeNode* root) {
        
        unordered_map<TreeNode*, int> count;
        stack<TreeNode*> stk;
        vector<int> traversal;
        
        stk.push(root);
        
        while(!stk.empty()) {
            TreeNode* cur = stk.top();
            if(!cur) {
                stk.pop();
                continue;
            }
            
            switch(count[cur]) {
                case 0:
                    stk.push(cur->left);
                    break;
                case 1:
                    traversal.push_back(cur->val);
                    break;
                case 2:
                    stk.push(cur->right);
                    break;
                default:
                    stk.pop();
                    break;
            }
            
            ++count[cur];
        }
        
        return traversal;
    }

iter_tree_trav1.cpp

    vector<int> inorderTraversal(TreeNode* root) {
        
        stack<pair<TreeNode*, int>> stk;
        vector<int> traversal;
        
        stk.push({root, 0});
        
        while(!stk.empty()) {
            auto [cur, state] = stk.top();
            stk.pop();
            
            if(!cur || state > 2) {
                continue;
            }
            
            stk.push({cur, state + 1});
            
            switch(state) {
                case 0:
                    stk.push({cur->left, 0});
                    break;
                case 1:
                    traversal.push_back(cur->val);
                    break;
                case 2:
                    stk.push({cur->right, 0});
                    break;
            }
        }
        
        return traversal;
    }