做这题的一个提升就是 先把recursive call当作能work的api.. 解决小问题先，再看小节 然后大问题其实就解决了
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23 | /**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public TreeNode upsideDownBinaryTree(TreeNode root) {
if (root == null || root.left == null){
return root;
}
TreeNode one = upsideDownBinaryTree(root.right);
TreeNode two = upsideDownBinaryTree(root.left);
root.left.left = one;
root.left.right = root;
root.left = null;
root.right = null;
return two;
}
}
|
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