CODE 112. Remove Nth Node From End of List

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版权声明：本文为博主原创文章，转载请注明出处：http://blog.jerkybible.com/2013/11/06/2013-11-06-CODE 112 Remove Nth Node From End of List/

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Given a linked list, remove the nth node from the end of list and return its head.
For example,
Given linked list: 1->2->3->4->5, and n = 2.

After removing the second node from the end, the linked list becomes 1->2->3->5.

Note:
Given n will always be valid.
Try to do this in one pass.

public ListNode removeNthFromEnd(ListNode head, int n) {
	// Start typing your Java solution below
	// DO NOT write main() function
	if (n < 1 || null == head) {
		return head;
	}
	ListNode pre = head;
	int i = 0;
	for (i = 1; i <= n && null != pre; i++) {
		pre = pre.next;
	}
	ListNode last = head;
	ListNode preLast = null;
	while (null != pre) {
		pre = pre.next;
		preLast = last;
		last = last.next;
	}
	if (null != preLast) {
		preLast.next = last.next;
	} else if (i == n + 1) {
		return head.next;
	} else {
		return head;
	}
	return head;
}