Leetcode 92. Reverse Linked List II (Medium) (cpp)

Leetcode 92. Reverse Linked List II (Medium) (cpp)

Tag: Linked List

Difficulty: Medium

/*

92. Reverse Linked List II (Medium)

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.

*/
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* reverseBetween(ListNode* head, int m, int n) {
ListNode *head_new = new ListNode(0);
head_new -> next = head;
ListNode *p = head_new;
int i = 1;
while (i < n) {
if (i++ < m) {
p = head;
head = head -> next;
} else {
ListNode *post = head -> next;
head -> next = head -> next -> next;
post -> next = p -> next;
p -> next = post;
}
}
return head_new -> next;
}
};