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struct TreeNode {
	int val;
	TreeNode *left;
	TreeNode *right;
	TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

class Node {
public:
	TreeNode* deleteNode(TreeNode* root, int key) {
		if (root == NULL) {
			return NULL;
		}
		if (key < root->val) {
			root->left = deleteNode(root->left, key);
		}
		else if (key > root->val) {
			root->right = deleteNode(root->right, key);
		}
		/* Cur node has to be deleted, handle 3 cases below */
		else {
			TreeNode * oldroot = root;
			// single or no child case.等价于 if (!root->left || !root->right) root = (!root->left) ? root->right : root->left;
			if (root->left == NULL) {
				return root->right;
			}
			else if (root->right == NULL) {
				return root->left;
			}
			/* Find smallest in right sub-tree, copy its val and delete it */
			else {
				TreeNode *minNode = findMin(root->right);
				root->val = minNode->val; /* curval = smallest in right subtree */
				root->right = deleteNode(root->right, root->val);
				/* next will already be deleted, nothing to del in this case */
				oldroot = NULL;
			}
			delete oldroot;
		}
		return root;
	}
private:
	/* Find the left-most node in the tree     */
	inline TreeNode *findMin(TreeNode *node) {
		while (node->left != NULL) {
			node = node->left;
		}
		return node;
	}
};

struct TreeNode {
	int val;
	TreeNode *left;
	TreeNode *right;
	TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

class Node {
public:
	TreeNode *deleteNode(TreeNode* root, int key) {
		if (root == NULL) {
			return NULL;
		}
		if (key < root->val) {			//key在左半树上
			root->left = deleteNode(root->left, key);
		}
		else if (key > root->val) {		//key在右半树上
			root->right = deleteNode(root->right, key);
		}
		else {							//当root->val等于NULL时，删除root
			TreeNode * oldroot = root;
			if (root->left == NULL) {
				return root->right;
			}
			else if (root->right == NULL) {
				return root->left;
			}
			else {		//we can chose root->left or root->right to be the new root in case it is not NULL.
				TreeNode *minNode = findMin(root->right);
				root->val = minNode->val;
				root->right = deleteNode(root->right, root->val);
				oldroot = NULL;
			}
			delete oldroot;
		}
		return root;
	}
private:
	TreeNode *findMin(TreeNode *node) {
		while (node->left != NULL) {
			node = node->left;
		}
		return node;
	}
};