86. Partition List【M】【48】【leetcode题解】

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.

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class Solution(object):
    def partition(self, head, x):
        h = head
        
        new_h = ListNode(0)
        new_head = new_h
        
        previous = ListNode(0)
        prv = previous
        #其中，pre是比x大的，h是比x小的
        prv.next = h#~!!!!!!!这句话非常重要！！因为最开始如果没有这句的话，就没有进行初始化，pre就只是一个空的头
        while h:
            if h.val < x:
                new_h.next = h
                new_h = h
                
                prv.next = h.next
                h = h.next
    
            else:
                prv = h
                h = h.next 
        new_h.next = previous.next
        return new_head.next