Binary Tree – 從入門到放棄

心得：

這題也是典型的遞迴，題目要求把二元樹整個翻轉過來。

問題：

Invert a binary tree.

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

1
2
3
4
5

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

to

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

1
2
3
4
5

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

答案：

遞迴

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode InvertTree(TreeNode root) {
        if(root == null){
            return null;
        }
        
        var left = root.left;
        var right = root.right;
        root.left = InvertTree(right);
        root.right = InvertTree(left);
        
        return root;
    }
}

/**

* Definition for a binary tree node.

* public class TreeNode {

* public int val;

* public TreeNode left;

* public TreeNode right;

* public TreeNode(int x) { val = x; }

* }

public class Solution {

public TreeNode InvertTree(TreeNode root) {

if(root == null){

return null;

}

var left = root.left;

var right = root.right;

root.left = InvertTree(right);

root.right = InvertTree(left);

return root;

}