[669. Trim a Binary Search Tree] #leetcode

669_0902.java

class Solution {
  // O(n) O(n)
    public TreeNode trimBST(TreeNode root, int L, int R) {
        if (root == null) return null;
        
        if (root.val > R) return trimBST(root.left, L, R);
        if (root.val < L) return trimBST(root.right, L, R);
        
        root.left = trimBST(root.left, L, root.val);
        root.right = trimBST(root.right, root.val, R);
        return root;
    }
}