701. Insert into a Binary Search Tree

题目

https://leetcode.com/problems/insert-into-a-binary-search-tree/

Given the root node of a binary search tree (BST) and a value to be inserted into the tree, insert the value into the BST. Return the root node of the BST after the insertion. It is guaranteed that the new value does not exist in the original BST.

Note that there may exist multiple valid ways for the insertion, as long as the tree remains a BST after insertion. You can return any of them.

For example,

Given the tree:

        4
       / \
      2   7
     / \
    1   3

And the value to insert: 5
You can return this binary search tree:

         4
       /   \
      2     7
     / \   /
    1   3 5

This tree is also valid:

         5
       /   \
      2     7
     / \   
    1   3
         \
          4

解答

额，凭着直觉，我认为，如果比当前节点大，并且右节点是空的，就塞进去，否则的话，就递归右节点。左节点一样的道理。然后写了一下代码，就通过了，还0ms beats 100%，太爽了……

public TreeNode insertIntoBST(TreeNode root, int val) {
    insert(root, val);
    return root;
}

public static void insert(TreeNode node, int val) {
    if (node != null) {
        if (val > node.val) {
            if (node.right == null) {
                node.right = new TreeNode(val);
            } else {
                insert(node.right, val);
            }
        } else if (val < node.val) {
            if (node.left == null) {
                node.left = new TreeNode(val);
            } else {
                insert(node.left, val);
            }
        }
    }
}