[LeetCode] 94 - Binary Tree Inorder Traversal

LeetCode Problem Link: https://leetcode.com/problems/binary-tree-inorder-traversal

Solution:
[1] Recursive
class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> result = new ArrayList<Integer>();
        if (root == null) return result;
        
        result.addAll(inorderTraversal(root.left));
        result.add(root.val);
        result.addAll(inorderTraversal(root.right));
        return result;
    }

}

[2] Iterative (using stack for DFS search)
class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> result = new ArrayList<Integer>();
        Stack<TreeNode> nodeStack = new Stack();
        TreeNode cur = root;
        while (cur != null || !nodeStack.empty()) {
            while (cur != null) {
                nodeStack.add(cur);
                cur = cur.left;
            }
            cur = nodeStack.pop();
            result.add(cur.val);
            cur = cur.right;
        }
        
        return result;
    }

}

Result:
Run time 2 ms
Beats 25% users