Leetcode Unique Binary Search Trees II

Unique Binary Search Trees II

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

confused what "{1,#,2,3}" means > read more on how binary tree is serialized on OJ.

五星级难度指数吧。

如何处理结束条件？

如果构造所有二叉排序树？

把递归放进循环里面的思想――这样就可以抽离根节点和左右子树节点

熟记这个思想，难度指数可以降低到4星级。

思想十分难，程序构造处理并不复杂。

//2014-2-15 update AC
	vector
  
    generateTrees(int n) 
	{
		return gen(1, n);
	}
	vector
   
     gen(int left, int right) { if (left > right) return vector
    
     (1, nullptr); vector
     
       rs; for (int k = left; k <= right; k++) { vector
      
        lt = gen(left, k-1); vector
       
         rt = gen(k+1, right); for (int i = 0; i < lt.size(); i++) { for (int j = 0; j < rt.size(); j++) { TreeNode *n = new TreeNode(k); n->left = lt[i]; n->right = rt[j]; rs.push_back(n); } } } return rs; }