Binary Tree Preorder Traversal
Given a binary tree, return the preorder traversal of its nodes' values.
For example:
Given binary tree {1,#,2,3}
,
1 \ 2 / 3
return [1,2,3]
.
Note: Recursive solution is trivial, could you do it iteratively?
/** * Definition for binary tree * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ public class Solution { public ArrayList<Integer> preorderTraversal(TreeNode root) { // IMPORTANT: Please reset any member data you declared, as // the same Solution instance will be reused for each test case. ArrayList<Integer> result = new ArrayList<Integer>(); Stack<TreeNode> stack = new Stack<TreeNode>(); if (root == null){ return result; } TreeNode t = null; stack.push(root); while (!stack.empty()&&(t = stack.pop())!=null){ result.add(t.val); if (t.right != null){ stack.add(t.right); } if (t.left != null){ stack.add(t.left); } } return result; } }