有序連結串列轉換二叉搜尋樹

這道題需要定義三個指標，通過快慢指標找出中點，作為根節點，然後從頭指標head->指標last這段連結串列再遞迴呼叫sortedListToBST函式，從slow指標下一個節點開始到最後，作為後一個連結串列再進行遞迴呼叫函式sortedListToBST函式。

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
 

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* sortedListToBST(ListNode* head) {
        if(head==NULL)
            return
 
 NULL;
        ListNode* fast=head;
        ListNode* slow=head;
        ListNode* last=head;
        while(fast->next && fast->next->next)
        {
            last=slow;
            slow=slow->next;
            fast=fast->next->next;
        }
        fast=slow->next;
 

        last->next=NULL;
        TreeNode *cur=new TreeNode(slow->val);
        if(head!=slow)
            cur->left=sortedListToBST(head);
            cur->right=sortedListToBST(fast);
         return cur;
    }
};