// Recursion
class Solution {
public:
TreeNode *upsideDownBinaryTree(TreeNode *root) {
if (!root || !root->left) return root;
TreeNode *l = root->left, *r = root->right;
TreeNode *res = upsideDownBinaryTree(l);
l->left = r;
l->right = root;
root->left = NULL;
root->right = NULL;
return res;
}
};
// Iterative
class Solution {
public:
TreeNode *upsideDownBinaryTree(TreeNode *root) {
TreeNode *cur = root, *pre = NULL, *next = NULL, *tmp = NULL;
while (cur) {
next = cur->left;
cur->left = tmp;
tmp = cur->right;
cur->right = pre;
pre = cur;
cur = next;
}
return pre;
}
};