Leetcode95 Unique Binary Search Trees II

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

1 /**2 * Definition for a binary tree node.3 * struct TreeNode {4 * int val;5 * TreeNode *left;6 * TreeNode *right;7 * TreeNode (int x): Val (x), left (null), right (null) {}8  * };9  */Ten classSolution { One  Public: AVector<treenode*> Generatetrees (intN) { -Vector<treenode*>ans; -Ans=generate (1, n); the         returnans; -     } -Vector<treenode*> Generate (intAintb) -     { +Vector<treenode*>ans; -         if(a>b) +             returnans; A         if(a==b) at         { -TreeNode *temp=NewTreeNode (a); - Ans.push_back (temp); -             returnans; -         } -Vector<treenode*> Vt1=generate (A +1, b); in          for(intI=0; I<vt1.size (); i++) -         { toTreeNode *tr1=NewTreeNode (a);//cannot be placed outside, otherwise, the TR1 in ans will become all the same. (TR1 same, tr1->right is different, therefore should be multi-points TR1) +tr1->right=Vt1[i]; - ans.push_back (TR1); the         } *          $Vector<treenode*> Vt2=generate (a,b-1);Panax Notoginseng          for(intI=0; I<vt2.size (); i++) -         { theTreeNode *tr2=NewTreeNode (b); +tr2->left=Vt2[i]; A Ans.push_back (TR2); the         } +          -          for(inti=a+1; i<=b-1; i++) $         { $Vector<treenode*> Vt31=generate (a,i-1); -Vector<treenode*> Vt32=generate (i+1, b); -              for(intj=0; J<vt31.size (); j + +) the             { -                  for(intk=0; K<vt32.size (); k++)Wuyi                 { theTreeNode *tr3=NewTreeNode (i); -tr3->left=Vt31[j]; Wutr3->right=Vt32[k]; - Ans.push_back (TR3); About                 } $             } -              -              -         } A         returnans; +     } the};

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Leetcode95 Unique Binary Search Trees II