92. Reverse Linked List II (List)

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.

class Solution {
public:
ListNode *reverseBetween(ListNode *head, int m, int n) {

if(!head || m==n ) return head;
ListNode * lastOfPrePart = head;
ListNode * preReverseNode;
ListNode * firstPostPart;
ListNode * nextReverseNode;
ListNode * currentReverseNode;

if(m>1)
{
for(int i = 0; i < m-2; i++)
{
lastOfPrePart = lastOfPrePart->next;
}
currentReverseNode = lastOfPrePart->next;
}
else
{
currentReverseNode = head;
}

nextReverseNode = currentReverseNode->next;
firstPostPart = currentReverseNode;
for(int i = m; i < n+1; i++ )
{
firstPostPart = firstPostPart -> next;
}

currentReverseNode ->next = firstPostPart;
while(nextReverseNode!= firstPostPart)
{
preReverseNode = currentReverseNode;
currentReverseNode = nextReverseNode;
nextReverseNode = currentReverseNode->next;
currentReverseNode->next = preReverseNode;
}
if(m!=1)
{
lastOfPrePart->next = currentReverseNode;
}
else
{
head = currentReverseNode;
}
return head;
}
};