LeetCode //C - 147. Insertion Sort List

147. Insertion Sort List

Given the head of a singly linked list, sort the list using insertion sort, and return the sorted list’s head.

The steps of the insertion sort algorithm:

1. Insertion sort iterates, consuming one input element each repetition and growing a sorted output list.
2. At each iteration, insertion sort removes one element from the input data, finds the location it belongs within the sorted list and inserts it there.
3. It repeats until no input elements remain.

The following is a graphical example of the insertion sort algorithm. The partially sorted list (black) initially contains only the first element in the list. One element (red) is removed from the input data and inserted in-place into the sorted list with each iteration.

 

Example 1:

Input: head = [4,2,1,3]
Output: [1,2,3,4]

Example 2:

Input: head = [-1,5,3,4,0]
Output: [-1,0,3,4,5]

Constraints:

• The number of nodes in the list is in the range [1, 5000].
• -5000 <= Node.val <= 5000

From: LeetCode
Link: 147. Insertion Sort List

Solution:

Ideas:

1. Node Definition and Creation:

• The ListNode structure defines a node in a singly linked list.
• The createNode function creates a new node with a given value.

2. Insertion Sort Function:

• The insertionSortList function sorts the linked list using the insertion sort algorithm.
• It iterates through each node in the original list, and inserts it into the correct position in the sorted list.

3. Helper Function:

• The printList function is used to print the values of the linked list nodes.

Code:

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode* createNode(int val) {
    struct ListNode* newNode = (struct ListNode*)malloc(sizeof(struct ListNode));
    newNode->val = val;
    newNode->next = NULL;
    return newNode;
}

struct ListNode* insertionSortList(struct ListNode* head) {
    if (!head) return NULL;
    
    struct ListNode* sorted = NULL;
    
    while (head) {
        struct ListNode* current = head;
        head = head->next;
        
        if (!sorted || sorted->val >= current->val) {
            current->next = sorted;
            sorted = current;
        } else {
            struct ListNode* temp = sorted;
            while (temp->next && temp->next->val < current->val) {
                temp = temp->next;
            }
            current->next = temp->next;
            temp->next = current;
        }
    }
    
    return sorted;
}

// Function to print the linked list
void printList(struct ListNode* head) {
    while (head) {
        printf("%d ", head->val);
        head = head->next;
    }
    printf("\n");
}