Leetcode 226.翻转二叉树

用递归，递归获取左右两树的根节点，然后替换左右两子树

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func invertTree(root *TreeNode) *TreeNode {
    if root == nil {
        return root
    }
    left := invertTree(root.Left)
    right := invertTree(root.Right)
    root.Left = right
    root.Right = left
    return root
}