LeetCode题解之Convert Sorted List to Binary Search Tree

1、题目描述

2、题目描述

使用快慢指针寻找链表中间值。

3、代码

TreeNode* sortedListToBST(ListNode* head) {
        if (head == NULL)
            return NULL;
        
        ListNode *mid = findmid(head);
        
        TreeNode *node = new TreeNode(mid->val);
        
        if (head == mid)
            return node;
        
        node->left = sortedListToBST(head);
        node->right = sortedListToBST(mid->next);
        return node;
        
    }
    
   
    
    ListNode *findmid(ListNode* left)
    {
        ListNode *preptr = NULL;
        ListNode *slow = left;
        ListNode *fast = left;
        
        while (fast != NULL && fast->next != NULL) {
            preptr = slow;
            slow = slow->next;
            fast = fast->next;
            fast = fast->next;
        }
        if (preptr != NULL)
            preptr->next = NULL;    
        return slow;
    }