Leetcode:unique Binary Search Trees II

Title Description:

Given n, generate all structurally unique BST 's (binary search trees) that store values 1 ... n.

For example,
Given N = 3, your program should return all 5 unique BST ' s shown below.

   1         3     3      2      1    \//      /\           3     2     1      1   3      2    /     /       \                    2     1         2                 3

Thinking Analysis: Let 1-n do root respectively. When Root is I, Zuozi is composed of 1~i-1 and the right subtree is composed of i+1~n. The recursive method is used to solve the left and right sub-trees, and then all possible solutions of the subtree are combined together to obtain all possible BST.

Code:

Vector<treenode *> gettrees (int start,int end) {    Vector<treenode *> result;    if (Start > End)    {        result.push_back (NULL);        return result;    }            if (start = = end)    {        TreeNode * new_node = new TreeNode (start);        Result.push_back (New_node);        return result;    }    for (int i = start;i <= end, i++)    {        Vector<treenode *> left = gettrees (start,i-1);        Vector<treenode *> right = Gettrees (i+1,end);        For (TreeNode * left_node:left) for            (TreeNode * right_node:right)        {            TreeNode * new_node = new TreeNode (i);            new_node->left = Left_node;            New_node->right = Right_node;            Result.push_back (New_node);        }    }    return result;} Vector<treenode *> solution::generatetrees (int n) {    return gettrees (1,n);}

Leetcode:unique Binary Search Trees II