LeetCode 450.Delete Node in a BST

public static class TreeNode {int val = 0;TreeNode left = null;TreeNode right = null;public TreeNode(int val) {this.val = val;}}public TreeNode findLeftMax(TreeNode root) {while (root.right != null) {root = root.right;}return root;}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);} else {if (root.left == null) {return root.right;}if (root.right == null) {return root.left;}TreeNode tp = findLeftMax(root.left);root.val = tp.val;root.left = deleteNode(root.left, root.val);}return root;}