[94. Binary Tree Inorder Traversal] #leetcode

94_0822.java

class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> result = new ArrayList<Integer>();
        
        Stack<TreeNode> stack = new Stack<TreeNode>();
        while ( !stack.isEmpty() || root != null ) {
            if ( root != null ) {
                stack.push(root);
                root = root.left;
            } else {
                TreeNode node = stack.pop();
                result.add(node.val);
                root = node.right;
            }
        }
        
        return result;
    }
}