[LeetCode] 61. Rotate List 解题思路

Given a list, rotate the list to the right by k places, where k is non-negative.

For example:
Given 1->2->3->4->5->NULL and k = 2,
return 4->5->1->2->3->NULL.

问题：给定列表 和一个整数 k ，旋转列表最后 k 个元素至列表最前面。

关键是找到最后元素 lastOne 和 旋转后列表新的最后元素 newLastOne

    ListNode* rotateRight(ListNode* head, int k) {
    
        if (head == NULL) {
            return NULL;
        }
        
        int n = 1;
        ListNode* lastOne = head;
        while (lastOne->next != NULL) {
            n++;
            lastOne = lastOne->next;
        }
        
        if (n == k) {
            return head;
        }
        
    　　int firstNum = n - (k % n);
                
        ListNode* newLastOne;
        newLastOne = head;
        for (int i = 1; i < firstNum; i++) {
            newLastOne = newLastOne->next;
        }
                
        lastOne->next = head;
        head = newLastOne->next;
        newLastOne->next = NULL;
        
        return head;
    }