leetcode 092 Reverse Linked List II

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.

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class Solution {
public:
ListNode* reverseBetween(ListNode* head, int m, int n) {
ListNode *lm=head, *pre=NULL, *ln=head, *temp=head;
for(int i=1; i<=n; i++) {
if(i < m) {
pre=lm;
lm=pre->next;
}
ln=temp;
temp=temp->next;
}

ListNode *next=ln->next;

for(int i=m; i<=n; i++) {
ListNode *lm_next = lm->next;
lm->next=next;
next = lm;
lm = lm_next;
}

if(pre!=NULL) {
pre->next=next;
} else {
head = next;
}

return head;
}
}