[leetcode] 86. Partition List

Description

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.

Example:
Input:

head = 1->4->3->2->5->2, x = 3

Output:

1->2->2->4->3->5

分析

题目的意思是：给定一个链表，一个数x，要求比x小的放在链表前面，大于等于x的放在链表后面。

• 只需要遍历一遍就行了，slow指针指向要插向的位置，fast来寻找需要移动的结点。

代码

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* partition(ListNode* head, int x) {
        if(!head) return head;
        ListNode* dummy=new ListNode(0);
        ListNode* slow=dummy;
        ListNode* fast=dummy;
        dummy->next=head;
        while(fast&&fast->next){
            if(fast->next->val>=x){
                fast=fast->next;
            }else{
                if(fast==slow){
                    fast=fast->next;
                    slow=slow->next;
                }else{
                    ListNode* temp=fast->next;
                    fast->next=temp->next;
                    temp->next=slow->next;
                    slow->next=temp;
                    slow=slow->next;
                }
                
            }
        }
        return dummy->next;
    }
};

参考文献

​​[编程题]partition-list​​