226. Invert Binary Tree My Submissions Question

题目

Invert a binary tree.

     4
   / \
  2 7
/ \ / \
1 3 6 9

to

     4
   / \
  7 2
/ \ / \
9 6 3 1

Trivia:

This problem was inspired by this original tweet by Max Howell:
Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so fuck off.

思路

每个节点下的子节点交换即可.

代码

# Definition for a binary tree node.
# class TreeNode
#     attr_accessor :val, :left, :right
#     def initialize(val)
#         @val = val
#         @left, @right = nil, nil
#     end
# end

# @param {TreeNode} root
# @return {TreeNode}
def invert_tree(root)
  if root == nil then return root end
  root.left,root.right = invert_tree(root.right),invert_tree(root.left)
  root
end