61. Rotate List(M);19. Remove Nth Node From End of List(M)

61. Rotate List(M)

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.

• Total Accepted: 102574
• Total Submissions: 423333
• Difficulty: Medium

/**
 * 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 == nullptr || k == 0) return head;
        int len = 1;
        ListNode* p = head;
        while (p->next) { //
            len++;
            p = p->next;
        }
        k = len - k % len;
        p->next = head; //
        for(int step = 0; step < k; step++) {
            p = p->next; //
        }
        head = p->next; //
        p->next = nullptr; //
        return head;
    }
};

16ms 19.35%

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {// by guxuanqing@gmail.com
public:
    ListNode* rotateRight(ListNode* head, int k)
    {
        if(NULL == head || NULL == head->next) return head;//null or one node
        ListNode *p = NULL, *q = head;
        int len = 1;
        while (q->next)//cal the length of the list
        {
           ++len;
            q = q->next;
        }
        q->next = head;
        k %= len;
        int tmp = len - k;
        q = head;
        while (--tmp)
        {
            q = q->next;
        }
        head = q->next;
        q->next = NULL;
        return head;
    }
};

19. Remove Nth Node From End of List

Given a linked list, remove the nth node from the end of list and return its head.

For example,

   Given linked list: 1->2->3->4->5, and n = 2.

   After removing the second node from the end, the linked list becomes 1->2->3->5.
Note:
Given n will always be valid.
Try to do this in one pass.

• Total Accepted: 169535
• Total Submissions: 517203
• Difficulty: Medium

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *removeNthFromEnd(ListNode *head, int n) {
        ListNode dummy(-1);
        dummy.next = head;
        ListNode *p = &dummy, *q = &dummy;
        for (int i = 0; i < n; i++)//q先走n步
            q = q->next;
        while(q->next) {
            p = p->next;
            q = q->next;
        }
        ListNode *tmp = p->next;
        p->next = p->next->next;
        delete tmp;
        return dummy.next;
    }
};

6ms 64.75%

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {// by guxuanqing@gmail.com
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        if(NULL == head || NULL == head->next) return NULL;//null or one node
        ListNode dummy(-1);
        dummy.next = head;
        ListNode *p = &dummy, *q = &dummy;
        int tmp = n;
        while (tmp--)
        {
            q = q->next;
        }
        while (q->next)
        {
            q = q->next;
            p = p->next;
        }
        ListNode *rnode = p->next;
        p->next = rnode->next;
        delete rnode;
        return dummy.next;
    }
};

9ms 23.47%