95_unique_binary_search_trees_II.java

import java.util.*;

class Solution {
    public List<TreeNode> generateTrees(int n) {
        if (n == 0)
            return new ArrayList<TreeNode>();
        return generateTrees(1, n);
    }

    List<TreeNode> generateTrees(int start, int end) {
        List<TreeNode> result = new ArrayList<TreeNode>(); // Missing parentheses for ArrayList constructor

        if (start > end) {
            result.add(null);
            return result;
        }

        for (int i = start; i <= end; i++) { // Changed "int" to "i" for loop condition
            List<TreeNode> leftSubTrees = generateTrees(start, i - 1); // Corrected function call
            List<TreeNode> rightSubTrees = generateTrees(i + 1, end); // Corrected function call

            for (TreeNode left : leftSubTrees) {
                for (TreeNode right : rightSubTrees) {
                    TreeNode root = new TreeNode(i);
                    root.left = left;
                    root.right = right;
                    result.add(root);
                }
            }
        }

        return result; // Added return statement
    }
}