175. Invert Binary Tree【LintCode by java】

Description

Invert a binary tree.

Example

  1         1
 / \       / \
2   3  => 3   2
   /       \
  4         4

 

 解题：题目要求讲二叉树的左子树和右子树对调一下，用递归来做很简单：

 /**
  * Definition of TreeNode:
  * public class TreeNode {
  *     public int val;
  *     public TreeNode left, right;
  *     public TreeNode(int val) {
  *         this.val = val;
  *         this.left = this.right = null;
  *     }
  * }
  */

 public class Solution {
     /**
      * @param root: a TreeNode, the root of the binary tree
      * @return: nothing
      */
     public void invertBinaryTree(TreeNode root) {
         // write your code here
         if(root == null)
             return ;
         TreeNode left = root.left;
         TreeNode right = root.right;
         root.left = right;
         root.right = left;
         invertBinaryTree(root.left);
         invertBinaryTree(root.right);
     }
 }

非递归法：

 public class Solution {
     public TreeNode invertTree(TreeNode root) {
         Queue<TreeNode> q = new LinkedList<TreeNode>();
         if(root!=null) q.offer(root);
         while(!q.isEmpty()){
             TreeNode curr = q.poll();
             TreeNode tmp = curr.right;
             curr.right = curr.left;
             curr.left = tmp;
             if(curr.left!=null) q.offer(curr.left);
             if(curr.right!=null) q.offer(curr.right);
         }
         return root;
     }
 }