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LeetCode: Partition List

LeetCode: Partition List

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.

地址:https://oj.leetcode.com/problems/partition-list/

算法:首先,找到第一个大于等于x的节点,记其前趋节点为pre,则在继续往后遍历,若发现比x小的值,则把该节点从链表中移出来,插入到pre节点后面。代码:

 1 /** 2  * Definition for singly-linked list. 3  * struct ListNode { 4  *     int val; 5  *     ListNode *next; 6  *     ListNode(int x) : val(x), next(NULL) {} 7  * }; 8  */ 9 class Solution {10 public:11     ListNode *partition(ListNode *head, int x) {12         if(!head)   return NULL;13         ListNode *p = head;14         ListNode *pre = NULL;15         while(p && p->val < x){16             pre = p;17             p = p->next;18         }19         if(!p)20             return head;21         ListNode *q = NULL;22         while(p->next){23             if(p->next->val < x){24                 q = p->next;25                 p->next = q->next;26                 if(pre){27                     q->next = pre->next;28                     pre->next = q;29                     pre = q;30                 }else{31                     q->next = head;32                     head = q;33                     pre = q;34                 }35             }else{36                 p = p->next;37             }38         }39         return head;40     }41 };

 

LeetCode: Partition List