Reverse Linked List II

07/07/2016 Linked List

Question

Reverse a linked list from position m to n. Do it in-place and in one-pass.

For example: Given 1->2->3->4->5->NULL, m = 2 and n = 4,

return 1->4->3->2->5->NULL.

Note:

Given m, n satisfy the following condition:

1 ≤ m ≤ n ≤ length of list.

Solution

Result: Accepted Time: 0 ms

Here should be some explanations.

struct ListNode* reverseBetween(struct ListNode* head, int m, int n) {
    if(m == n)
        return head;
    struct ListNode Head;
    Head.next = head;
    struct ListNode * now = head, *last = &Head,*tmp;
    struct ListNode ptr;
    ptr.next = NULL;
    int cnt = 1;
    while(cnt < m)
    {
        last = now;
        now = now -> next;
        cnt++;
    }
    while(cnt <= n)
    {
        tmp = now;
        now = now->next;
        tmp -> next  = ptr.next;
        ptr.next = tmp;
        cnt++;
    }
    last->next -> next = now;
    last->next = ptr.next;
    return Head.next;
}

Complexity Analytics

  • Time Complexity:
  • Space Complexity: