二叉搜索树的生成

给定一个整数 n，生成所有由 1 ... n 为节点所组成的 二叉搜索树 。

https://leetcode-cn.com/problems/unique-binary-search-trees-ii/

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {number} n
 * @return {TreeNode[]}
 */
var generateTrees = function(n) {
    
    var buildTree=function(start,end){
         
         var trees=[]
         if(start>end){
             return [null]
         }
         for(var i=start;i<=end;i++){
             var left=buildTree(start,i-1)
             var right=buildTree(i+1,end)
             for(var leftNode of left){
                 for(var rightNode of right){
                     var node=new TreeNode(i)
                     node.left=leftNode;
                     node.right=rightNode;
                     trees.push(node)
                 }
             }
         }
         return trees;
    }
    if(n===0){
        return []
    }
    return buildTree(1,n)
};