Rotate List Solutions in C++

// Source : https://oj.leetcode.com/problems/rotate-list/
// Author : Hao Chen
// Date   : 2014-06-20



/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *rotateRight(ListNode *head, int k) {
        if (!head || k<=0){
            return head;
        }
        
        //find the length of List
        int len=1;
        ListNode *p=head;
        while( p->next != NULL ){
            p = p->next;
            len++;
        }
        //connect the tail to head
        p->next = head;
        //find the left place (take care the case - k > len)
        k = len - k % len;
        
        //find the place
        for(int i=0; i<k; i++){
            p = p->next;
        }
        
        //break the list
        head = p->next;
        p->next = NULL;
        
        return head;
        
    }
};

#include <cstddef>

struct ListNode {
    int val;
    ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};

class Solution {
public:
    ListNode *rotateRight(ListNode *head, int k) {
        if (head == NULL || k == 0) return head;
        ListNode *slow = head, *fast = head;
        while (k--) {
            if (fast == NULL) fast = head;
            fast = fast->next;
        }
        if (fast == NULL) return head;
        while (fast->next) {
            fast = fast->next;
            slow = slow->next;
        }
        ListNode *new_head = slow->next;
        slow->next = NULL;
        fast->next = head;
        return new_head;
    }
};

/// Source : https://leetcode.com/problems/rotate-list/description/
/// Author : liuyubobobo
/// Time   : 2018-03-18

#include <iostream>

using namespace std;


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

/// Brute Force
/// Two Pointers
///
/// Time Complexity: O(N)
/// Space Complexity: O(1)
class Solution {
public:
    ListNode* rotateRight(ListNode* head, int k) {

        if(head == NULL)
            return NULL;

        int len = get_len(head);
        k = k % len;

        ListNode* end = head;
        for(int i = 0 ; i < k ; i ++)
            end = end->next;

        ListNode* start = head;
        while(end->next != NULL){
            start = start->next;
            end = end->next;
        }

        end->next = head;
        head = start->next;
        start->next = NULL;

        return head;
    }

private:
    int get_len(ListNode* head){
        int res = 0;
        while(head){
            res ++;
            head = head->next;
        }
        return res;
    }
};


int main() {

    return 0;
}