LeetCode Covert 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.

Tips:

Use two pointers to find the middle element in the forward_list.

Solution:

/**
 * 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:
    void build(TreeNode*& root,ListNode *head,ListNode *tail){
        if(head==tail)
            return;
        ListNode *t1=head,*t2=head;
        while(t2!=tail){
            t2=t2->next;
            if(t2!=tail)
                t2=t2->next;
            else 
                break;
            t1=t1->next;
        }
        root=new TreeNode(t1->val);
        build(root->left,head,t1);
        build(root->right,t1->next,tail);
    }

    TreeNode *sortedListToBST(ListNode *head) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(!head)
            return NULL;
        TreeNode* result=NULL;
        build(result,head,NULL);
        return result;
    }
};