leetcode 链表 Partition List

Partition List

 Total Accepted: 19761 Total Submissions: 73252My Submissions

Given a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x.

You should preserve the original relative order of the nodes in each of the two partitions.

For example,
Given 1->4->3->2->5->2 and x = 3,
return 1->2->2->4->3->5.

题意：依据给定值x划分链表。使得比x小的值排在前面。要求保持元素原先的相对位置。

思路：
维护两个链表，一个是比x小的节点的链表l1，还有一个是大于等于x的节点的链表l2
最后把l1的尾部接到l2的头部


复杂度：时间O(n)。空间O(1)

ListNode *partition(ListNode *head, int x) {
	ListNode less(-1), larger_equal(-1);
	ListNode *less_ptr = &less, *larger_equal_ptr = &larger_equal;
	for (ListNode *cur = head; cur != NULL; cur = cur->next)
	{
		if(cur->val < x){
			less_ptr = less_ptr->next = cur;
		}else{
			larger_equal_ptr = larger_equal_ptr->next = cur;
		}
	}
	less_ptr->next = larger_equal.next;
	larger_equal_ptr->next = NULL;
	return less.next;
}