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?
源碼:Java版本/** * Definition for binary tree * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ public class Solution { public ListpreorderTraversal(TreeNode root) { List result=new ArrayList (); Stack stack=new Stack(); TreeNode node=root; do { while(node!=null) { result.add(node.val); if(node.right!=null) { stack.push(node.right); } node=node.left; } if(!stack.isEmpty()) { node=stack.pop(); } }while(!stack.isEmpty() || node!=null); return result; } }