Binary Tree Upside Down
Given a binary tree where all the right nodes are either leaf nodes with a sibling (a left node that shares the same parent node) or empty, flip it upside down and turn it into a tree where the original right nodes turned into left leaf nodes. Return the new root.
For example:
Given a binary tree {1,2,3,4,5}
,
1 / \ 2 3 / \ 4 5
return the root of the binary tree [4,5,2,#,#,3,1]
.
4 / \ 5 2 / \ 3 1
将left node 入stack, 然后将每个原来的left node的 left = parent.right, right = parent. (从下往上做)
1 /** 2 * Definition for binary tree 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */ 10 public class Solution { 11 public TreeNode UpsideDownBinaryTree(TreeNode root) { 12 if(root == null) return root; 13 LinkedList<TreeNode> ll = new LinkedList<TreeNode> (); 14 ll.push(root); 15 while(root.left != null){ 16 ll.push(root.left); 17 root = root.left; 18 } 19 while(!ll.isEmpty()){ 20 TreeNode tmp = ll.pop(); 21 tmp.right = ll.peek(); 22 tmp.left = ll.peek() == null ? null : ll.peek().right; 23 } 24 return root; 25 } 26 }
从上往下做:
1 public class Solution { 2 public TreeNode UpsideDownBinaryTree(TreeNode root) { 3 if(root == null) return root; 4 TreeNode cur = root, last = null, lastRight = null; 5 while(cur != null){ 6 TreeNode tmp = cur.left; 7 cur.left = lastRight; 8 lastRight = cur.right; 9 cur.right = last; 10 last = cur; 11 cur = tmp; 12 } 13 return last; 14 } 15 }
posted on 2015-01-19 14:26 Step-BY-Step 阅读(212) 评论(0) 编辑 收藏 举报