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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?
答案
/** * Definition for binary tree * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ public class Solution { public List<Integer> preorderTraversal(TreeNode root) { List<Integer> result=null; if(root==null) { result=new LinkedList<Integer>(); return result; } if(root.left==null&&root.right==null) { result=new LinkedList<Integer>(); result.add(root.val); return result; } if(root.left!=null) { result=preorderTraversal(root.left); } if(root.right!=null) { List<Integer> right=preorderTraversal(root.right); if(result==null) { result=right; } else { result.addAll(right); } } result.add(0,root.val); return result; } }
Binary Tree Preorder Traversal
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