[LeetCode] Partition List

最新推荐文章于 2019-07-16 09:33:43 发布

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最新推荐文章于 2019-07-16 09:33:43 发布

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本文介绍了一种链表partition算法，通过维护三个指针，将链表中小于指定值x的节点放在左侧，大于等于x的节点放在右侧，同时保持各部分节点的原始相对顺序不变。

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.

链表的partition,也就是链表的快排，保存三个指针，一个指针指向当前链表，一个指针指向小于x的左链表，一个指针指向大于等于x的右链表

不断移动这三个指针，最后将右链表尾部置NULL,左链表指向右链表头部

/**
 * 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) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        ListNode *ldummy = new ListNode(-1);
        ListNode *rdummy = new ListNode(-1);
        ListNode *lp = ldummy, *rp = rdummy, *cur = head;
        while(cur != NULL) {
            if(cur->val < x) {
                lp->next = cur;
                lp = lp->next;
                cur = cur->next;
            }
            else {
                rp->next = cur;
                rp = rp->next;
                cur = cur->next;
            }
        }
        rp->next = NULL;
        lp->next = rdummy->next;
        return ldummy->next;
    }
};