Here, We see Unique Binary Search Trees II LeetCode Solution. This Leetcode problem is done in many programming languages like C++, Java, JavaScript, Python etc. with different approaches.

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Unique Binary Search Trees II LeetCode Solution

Problem Statement

Given an integer n, return all the structurally unique BST’s (binary search trees), which has exactly n nodes of unique values from 1 to n. Return the answer in any order.

Example 1:

Input: n = 3
Output: [[1,null,2,null,3],[1,null,3,2],[2,1,3],[3,1,null,null,2],[3,2,null,1]]

Example 2:

Input: n = 1
Output: [[1]]

Unique Binary Search Trees II Leetcode Solution C++

class Solution {
public:
    vector<TreeNode*> generateTrees(int n) {
        	if(n == 0)	return vector<TreeNode *>(1, NULL);
	vector<vector<vector<TreeNode*>>> subtree(n+2, vector<vector<TreeNode*>>(n+2, vector<TreeNode*>()));
	for(int i=1; i<=n+1; ++i){
		subtree[i][i].push_back(new TreeNode(i));
	    subtree[i][i-1].push_back(NULL);	
	}
	for(int l=2; l<=n; ++l){
		for(int i=1; i<=n-l+1; ++i){
			for(int j=i; j<=i+l-1; ++j){
				for(int k=0; k<subtree[j+1][i+l-1].size(); ++k){
				    for(int m=0; m<subtree[i][j-1].size(); ++m){
				        TreeNode *T = new TreeNode(j);
				        T->left = subtree[i][j-1][m];
				        T->right = subtree[j+1][i+l-1][k];
			            subtree[i][i+l-1].push_back(T);    
				    }
				}
			}
		}
	}
	return subtree[1][n];
    }
};Code language: PHP (php)

Unique Binary Search Trees II Leetcode Solution Java

class Solution {
    public List<TreeNode> generateTrees(int n) {
         return generateTrees(1,n);
 }

public List<TreeNode> generateTrees(int start,int end){             
    List<TreeNode> trees = new ArrayList<TreeNode>();
    if(start>end){  trees.add(null); return trees;}

    for(int rootValue=start;rootValue<=end;rootValue++){
        List<TreeNode> leftSubTrees=generateTrees(start,rootValue-1);
        List<TreeNode> rightSubTrees=generateTrees(rootValue+1,end);

        for(TreeNode leftSubTree:leftSubTrees){
            for(TreeNode rightSubTree:rightSubTrees){
                TreeNode root=new TreeNode(rootValue);
                root.left=leftSubTree;
                root.right=rightSubTree;
                trees.add(root);
            }
        }
    }
    return trees;    
    }
}Code language: PHP (php)

Unique Binary Search Trees II Leetcode Solution JavaScript

var generateTrees = function(n) {
    const constructArray = (start, end) => {
        const result = [];
        
        if(start > end){
            return [null];
        }
        
        if(start===end){
            return [new TreeNode(start)];
        }
        
        if(end-start===1){
            const first = new TreeNode(start, null, new TreeNode(end));
            const second = new TreeNode(end, new TreeNode(start), null);
            return [first, second];
        }
        
        for(let i=start; i<=end; i++){
            const leftSide = constructArray(start, i-1);
            const rightSide = constructArray(i+1, end);
            
            leftSide.forEach(ls => {
                rightSide.forEach(rs => {
                    const tree = new TreeNode(i, ls, rs);
                    
                    result.push(tree);
                })
            })
        }
        return result;
    }
    return constructArray(1,n); 
};Code language: JavaScript (javascript)

Unique Binary Search Trees II Leetcode Solution Python

class Solution(object):
    def generateTrees(self, n):
        def node(val, left, right):
            node = TreeNode(val)
            node.left = left
            node.right = right
            return node
        def trees(first, last):
            return [node(root, left, right)
                    for root in range(first, last+1)
                    for left in trees(first, root-1)
                    for right in trees(root+1, last)] or [None]
        return trees(1, n)