LEETCODE: Partition List

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最新推荐文章于 2025-07-08 17:08:10 发布

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文章标签： LEETCODE 算法指针

本文链接：https://blog.youkuaiyun.com/anyicheng2015/article/details/42193117

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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。通过具体的代码实现展示了如何操作链表指针来完成这一任务。

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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.

关于指针的操作！需要熟练，多做久好了。

/**
 * 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 == NULL || head->next == NULL)  return head;
        ListNode *newHead = NULL;
        ListNode *smaller = NULL;
        ListNode *largehead = NULL;
        ListNode *larger = NULL;
        while(head != NULL) {
            if(head->val < x) {
                if(smaller == NULL) {
                    smaller = head;
                    newHead = head;
                }
                else {
                    smaller->next = head;
                    smaller = smaller->next;
                }
            }
            else {
                if(larger == NULL) {
                    larger = head;
                    largehead = head;
                }
                else {
                    larger->next = head;
                    larger = larger->next;
                }
            }
            head = head->next;
        }
        
        if(larger != NULL) {
            larger->next = NULL;
        }
        
        if(smaller != NULL) {
            smaller->next = largehead;
            return newHead;
        }
        
        return largehead;
    }
};