【leetcode】Convert Sorted List to Binary Search Tree

Convert Sorted List to Binary Search Tree

Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.

 

 

可以采用类似于Covert Sorted Array to Binary Search Tree的方法，但是寻找中点对于链表来说效率较低

可以采用更高效的递归方式，无需寻找中点

注意引用传递：TreeNode *buildTree(ListNode *&node,int left,int right)

 

 /**
  * Definition for singly-linked list.
  * struct ListNode {
  *     int val;
  *     ListNode *next;
  *     ListNode(int x) : val(x), next(NULL) {}
  * };
  */
 /**
  * Definition for binary tree
  * struct TreeNode {
  *     int val;
  *     TreeNode *left;
  *     TreeNode *right;
  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
  * };
  */
 class Solution {
 public:
     TreeNode *sortedListToBST(ListNode *head) {

         ListNode *p=head;
         int len=;
         while(p!=NULL)
         {
             p=p->next;
             len++;
         }

         TreeNode * root=buildTree(head,,len-);
         return root;

     }

     TreeNode *buildTree(ListNode *&node,int left,int right)
     {
         if(left>right) return NULL;

         int mid=(left+right)/;

         TreeNode *leftTree=buildTree(node,left,mid-);
         TreeNode *root=new TreeNode(node->val);
         node=node->next;
         TreeNode *rightTree=buildTree(node,mid+,right);
         root->left=leftTree;
         root->right=rightTree;
         return root;
     }

 };