[LeetCode] 144. Binary Tree Preorder Traversal

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

Preorder Traversal은

 

Visit, Left, Right의 순서로 기억하면 된다.