_776.java

package com.fishercoder.solutions;

import com.fishercoder.common.classes.TreeNode;

/**
 * 776. Split BST
 *
 * Given a Binary Search Tree (BST) with root node root, and a target value V,
 * split the tree into two subtrees where one subtree has nodes that are all smaller or equal to the target value,
 * while the other subtree has all nodes that are greater than the target value.
 * It's not necessarily the case that the tree contains a node with value V.
 * Additionally, most of the structure of the original tree should remain.
 * Formally, for any child C with parent P in the original tree,
 * if they are both in the same subtree after the split, then node C should still have the parent P.
 * You should output the root TreeNode of both subtrees after splitting, in any order.

 Example 1:

 Input: root = [4,2,6,1,3,5,7], V = 2
 Output: [[2,1],[4,3,6,null,null,5,7]]

 Explanation:
 Note that root, output[0], and output[1] are TreeNode objects, not arrays.

 The given tree [4,2,6,1,3,5,7] is represented by the following diagram:

       4
    /     \
   2      6
  /  \   / \
 1   3  5   7

 while the diagrams for the outputs are:

   4
 /   \
3     6      and    2
     / \           /
    5   7         1

 Note:

 The size of the BST will not exceed 50.
 The BST is always valid and each node's value is different.
 */

public class _776 {
  public static class Solution1 {
    /** credit: https://discuss.leetcode.com/topic/119481/recursive-java-solution */
    public TreeNode[] splitBST(TreeNode root, int V) {
      TreeNode small = new TreeNode(0);
      TreeNode big = new TreeNode(0);
      split(root, V, small, big);
      return new TreeNode[] {small.right, big.left};
    }

    private void split(TreeNode root, int v, TreeNode small, TreeNode big) {
      if (root == null) {
        return;
      }
      if (root.val <= v) {
        small.right = root;
        TreeNode right = root.right;
        root.right = null;
        split(right, v, root, big);
      } else {
        big.left = root;
        TreeNode left = root.left;
        root.left = null;
        split(left, v, small, root);
      }
    }
  }

  public static class Solution2 {
    /** credit: https://leetcode.com/articles/split-bst/ */
    public TreeNode[] splitBST(TreeNode root, int V) {
      if (root == null) {
        return new TreeNode[] {null, null};
      } else if (root.val <= V) {
        TreeNode[] result = splitBST(root.right, V);
        root.right = result[0];
        result[0] = root;
        return result;
      } else {
        TreeNode[] result = splitBST(root.left, V);
        root.left = result[1];
        result[1] = root;
        return result;
      }
    }
  }
}