trim-a-binary-search-tree.java

/**
 * Definition for a binary tree node. public class TreeNode { int val; TreeNode
 * left; TreeNode right; TreeNode() {} TreeNode(int val) { this.val = val; }
 * TreeNode(int val, TreeNode left, TreeNode right) { this.val = val; this.left
 * = left; this.right = right; } }
 */
class Solution {
  public TreeNode trimBST(TreeNode root, int low, int high) {
    if (root == null) {
      return null;
    }

    if (root.val < low) {
      return trimBST(root.right, low, high);
    }

    if (root.val > high) {
      return trimBST(root.left, low, high);
    }

    root.left = trimBST(root.left, low, high);
    root.right = trimBST(root.right, low, high);

    return root;
  }
}