public ListNode reverseBetween(ListNode head, int m, int n) {
if(head==null) return head;
ListNode slow = head;
ListNode fast = head;
//find middle
while(fast.next!=null) {
fast = fast.next;
if(fast.next!=null) {
fast = fast.next;
}
else {
slow = slow.next;
}
}
ListNode current = slow.next;
ListNode halfFirst = current;
if(current == null || current.next==null) {
return head;
}
ListNode next = current.next;
// reverse
while(next!=null) {
ListNode temp = current;
current = next;
next = next.next;
current.next = temp;
}
//combine
slow.next = current;
halfFirst.next = null;
return head;
}
amazon o2 - reverse second half linked list
原文：http://www.cnblogs.com/marc-leetcode/p/5139229.html