void recoverTreeHelper(TreeNode *curNode, TreeNode *&preNode, TreeNode *&first, TreeNode *&second) {
if (curNode == NULL) return;
recoverTreeHelper(curNode->left, preNode, first, second);
if (preNode && preNode->val > curNode->val) {
if (first == NULL) first = preNode;
second = curNode;
}
preNode = curNode;
recoverTreeHelper(curNode->right, preNode, first, second);
}
void recoverTree(TreeNode *root) {
n1 = n2 = prev = NULL;
recoverTreeHelper(root);
if (n1 && n2) {
swap(n1->val, n2->val);
}
}
void recoverTreeHelper(TreeNode *root) {
if (root == NULL) return;
recoverTreeHelper(root->left);
if (prev) {
if (prev->val > root->val){
if (n1==NULL) {
n1 = prev;
}
n2 = root;
}
}
prev = root;
recoverTreeHelper(root->right);
}
void recoverTree(TreeNode *root) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
TreeNode *prev = NULL, *first = NULL, *second = NULL;
recoverTreeHelper(root, prev, first, second);
swap(first->val, second->val);
}
