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
Given 1->4->3->2->5->2->null and x = 3,
return 1->2->2->4->3->5->null.

Link

Lintcode_ladder

Method

1. create two dummy lists, then trying to append them
2. x

Example

1. 1

/**
 * Definition of ListNode
 * class ListNode {
 * public:
 *     int val;
 *     ListNode *next;
 *     ListNode(int val) {
 *         this->val = val;
 *         this->next = NULL;
 *     }
 * }
 */
class Solution {
public:
    /**
     * @param head: The first node of linked list.
     * @param x: an integer
     * @return: a ListNode 
     */
    ListNode *partition(ListNode *head, int x) {
        // write your code here
        if (!head) {
            return nullptr;
        }
        ListNode dummy1(INT_MIN);
        ListNode dummy2(INT_MIN);
        ListNode* less_head = &dummy1;
        ListNode* more_head = &dummy2;
        ListNode* less = &dummy1;
        ListNode* more = &dummy2;
        ListNode* cur = head;
        while (cur) {
            if (cur->val < x) {
                less->next = new ListNode(cur->val);
                less = less->next;
            } else {
                more->next = new ListNode(cur->val);
                more = more->next;
            }
            cur = cur->next;
        }
        less->next = more_head->next;
        return less_head->next;
    }
};

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