701. Insert into a Binary Search Tree

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

/*
Iterative Solution

Time Complexity: O(N) - If the tree is skewed it will visit all nodes.
Space Complexity: O(1)
N = Total number of nodes in the binary search tree.
*/
class Solution {
    public TreeNode insertIntoBST(TreeNode root, int val) throws IllegalArgumentException {
        if (root == null) {
            return new TreeNode(val);
        }
        TreeNode cur = root;
        while (true) {
            if (val == cur.val) {
                throw new IllegalArgumentException("val already exists in the given binary search tree");
            }
            if (val > cur.val) {
                if (cur.right != null) {
                    cur = cur.right;
                } else {
                    cur.right = new TreeNode(val);
                    break;
                }
            } else {
                if (cur.left != null) {
                    cur = cur.left;
                } else {
                    cur.left = new TreeNode(val);
                    break;
                }
            }
        }
        return root;
    }
}


/*
Recursive Solution

Time Complexity: O(N) - If the tree is skewed it will visit all nodes.
Space Complexity: O(H)
N = Total number of nodes in the binary search tree.
H = Height of the tree (Recursion Stack).
*/
class Solution {
    public TreeNode insertIntoBST(TreeNode root, int val) throws IllegalArgumentException {
        if (root == null) {
            return new TreeNode(val);
        }
        if (val == root.val) {
            throw new IllegalArgumentException("val already exists in the given binary search tree");
        }
        if (val > root.val) {
            root.right = insertIntoBST(root.right, val);
        } else {
            root.left = insertIntoBST(root.left, val);
        }
        return root;
    }
}