leetcode[109]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.

/**
 * 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 *creatTree(ListNode *&head, int left, int right)
{
    if(left>right)return NULL;
    int mid=(left+right)/2;
    TreeNode *treeLeft=creatTree(head,left,mid-1);
    TreeNode *root=new TreeNode(head->val);    
    root->left=treeLeft;
    head=head->next;
    root->right=creatTree(head,mid+1,right);
}
TreeNode *sortedListToBST(ListNode *head) {
    TreeNode *root;
    int len=0;
    ListNode *tmp=head;
    while(tmp)
    {
        len++;
        tmp=tmp->next;
    }
    root=creatTree(head, 0, len-1);
}
/*
void creatTree(TreeNode *&root,vector<int> &num,int left,int right)
{
    if(left>right)return;
    int mid=(left+right)/2;
    root=new TreeNode(num[mid]);
    creatTree(root->left,num,left,mid-1);
    creatTree(root->right,num,mid+1,right);
}
TreeNode *sortedArrayToBST(vector<int> &num) 
{
    TreeNode *root=NULL;
    creatTree(root,num,0,num.size()-1);
    return root;
}
    TreeNode *sortedListToBST(ListNode *head) {
        TreeNode *root=NULL;
        if(head==NULL)return root;
        vector<int> num;
        while(head)
        {
            num.push_back(head->val);
            head=head->next;
        }
        return sortedArrayToBST(num);
    }
*/
};