Today I have done leetcode's March LeetCoding Challenge with cpp.

March LeetCoding Challenge 11

Description

Rotate List

Given the head of a linked list, rotate the list to the right by k places.

Example 1:

Input: head = [1,2,3,4,5], k = 2
Output: [4,5,1,2,3]

Example 2:

Input: head = [0,1,2], k = 4
Output: [2,0,1]

Constraints:

• The number of nodes in the list is in the range [0, 500].
• -100 <= Node.val <= 100
• 0 <= k <= 2 * 10^9

Solution

class Solution {
  int length(ListNode* head) {
    ListNode *cur = head;
    int len = 0;
    while(cur) {
        cur = cur->next;
        len += 1;
    }
    return len;
  }
public:
  ListNode* rotateRight(ListNode* head, int k) {
    int len = length(head);
    if(!len || k%len == 0) return head;
    k = len - (k % len);
    ListNode *cur = head, *previous;
    while(k--) {
      previous = cur;
      cur = cur->next;
    }
    ListNode *new_head = cur;
    while(cur->next) cur = cur->next;
    cur->next = head;
    previous->next = NULL;
    return new_head;
  }
};

// Accepted
// 231/231 cases passed (16 ms)
// Your runtime beats 22.86 % of cpp submissions
// Your memory usage beats 55.87 % of cpp submissions (11.8 MB)