題目226. Invert Binary Tree

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.

1,遞歸

思路:遞歸的交換左右子樹

public class Solution {
    public TreeNode invertTree(TreeNode root) {
        dfs(root);
        return root;
    }
    
    private void dfs(TreeNode root){
        if(root == null){
            return;
        }
        
        TreeNode temp = root.left;
        root.left = root.right;
        root.right = temp;
        
        dfs(root.left);
        dfs(root.right);
    }
}