Algorithm_Linked List

Sort List Problem

For God’s sake, don’t try sorting a linked list during the interview

So it might be better to actually copy the values into an array and sort them there.

Tip:
Since a node may be inserted before head, we can create a new_head that points to head.

Insertion Sort List:

My version:

ListNode* insertionSortList(ListNode* head) {    if(head == NULL) return head;    ListNode* new_head = new ListNode(numeric_limits<int>::min());    new_head->next = head;    ListNode* right = head->next;    head->next = NULL;    while(right){        ListNode* rnext = right->next;        right->next = NULL;        ListNode* p = new_head;        while(p){            if(p->next != NULL && p->next->val > right->val && p->val <= right->val){                right->next = p->next;                p->next = right;                break;            }            if(p->next == NULL){                p->next = right;                break;            }            p = p->next;        }        right = rnext;    }    head = new_head->next;    delete(new_head);    return head;}

Better version:

ListNode* insertionSortList(ListNode* head) {    ListNode* new_head = new ListNode(0);    new_head -> next = head;    ListNode* pre = new_head;    ListNode* cur = head;    while (cur) {        if (cur -> next && cur -> next -> val < cur -> val) {            while (pre -> next && pre -> next -> val < cur -> next -> val)                pre = pre -> next;            /* Insert cur -> next after pre.*/            ListNode* temp = pre -> next;            pre -> next = cur -> next;            cur -> next = cur -> next -> next;            pre -> next -> next = temp;            /* Move pre back to new_head. */            pre = new_head;        }        else cur = cur -> next;    }    ListNode* res = new_head -> next;    delete new_head;    return res;}