Leetcode: Insertion Sort List

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution
{
public:
    ListNode *insertionSortList(ListNode *head)
    {
        if (!head) return nullptr;
        //previous记住当前节点的前一个节点（因为单链表进行插入操作的时候必须知道当前节点的前一个节点）
        ListNode *previous = head;
        //current节点是要往前面已经排好序的节点中进行插入的节点
        ListNode *current = head->next;
        while (current)
        {
            //small和big指针用于记录比current小和比current大的指针，small和big相邻
            ListNode *small = nullptr;
            ListNode *big = head;
            while (big->val < current->val)
            {
                small = big;
                big = big->next;
            }
            //如果big!=current说明current节点应该插入到small和big节点之间
            if (big != current)
            {
                previous->next = current->next;
                if (small) small->next = current;
                else head = current;
                current->next = big;
            }
            //如果big=current这时previous指向下一个节点就OK了
            else
            {
                previous = previous->next;
            }
            //最后current节点指向previous下一个节点即current向前走一步
            current = previous->next;
        }
        return head;
    }
};

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode insertionSortList(ListNode head) {
        if (head == null) return null;
        ListNode previous = head;
        ListNode current = head.next;
        while (current != null) {
            ListNode small = null;
            ListNode big = head;
            //找出介于current的big和small元素，big和small相邻
            while (big.val < current.val) {
                small = big;
                big = big.next;
            }
            //如果big!=current将current插入到small和big之间
            if (big != current) {
                previous.next = current.next;
                if (small != null) small.next = current;
                else head = current;
                current.next = big;
            } else {
                previous = previous.next;
            }
            current = previous.next;
        }
        return head;
    }
}