[Leetcode] Partition List

最新推荐文章于 2019-07-16 09:33:43 发布

原创最新推荐文章于 2019-07-16 09:33:43 发布 · 468 阅读

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本文介绍了一种链表分区算法，该算法将链表中小于给定值x的所有节点置于大于等于x的节点之前，同时保持各分区内部节点的原始相对顺序不变。例如，对于链表1->4->3->2->5->2和x=3，算法返回1->2->2->4->3->5。代码实现使用了两个虚拟头结点来分别构建小于x和大于等于x的节点链表。

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.

/**
 * 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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(!head) return NULL;
        
        ListNode *smallVir = new ListNode(-1);
        ListNode *greatVir = new ListNode(-1);
        
        ListNode *smallPtr = smallVir; //Virtual head for smaller list
        ListNode *greatPtr = greatVir;
        ListNode *curPtr   = head;
        
        while(curPtr!=NULL)
        {
            
            if(curPtr->val<x)
            {
                smallPtr->next = curPtr;
                smallPtr = curPtr;
            }
            else
            {
                greatPtr->next= curPtr;
                greatPtr = curPtr;                
            }

            curPtr = curPtr->next;
            
        }
        
        greatPtr->next = NULL;//重要，新链表的末尾不一定是旧链表的末尾
        smallPtr->next = (greatVir->next)?greatVir->next:NULL;
        return smallVir->next;
    }
};