How Insertion Sort Works

Insertion Sort works the way you sort playing cards in your hands: you iterate through the array, pick the current element (key), and insert it into its correct relative position within the already-sorted prefix on the left by shifting larger elements one position to the right.

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C Code Implementation

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>

void insertionSort(int arr[], int n) {
    for (int i = 1; i < n; i++) {
        int key = arr[i];
        int j = i - 1;

        /* Shift elements greater than key to one position ahead */
        while (j >= 0 && arr[j] > key) {
            arr[j + 1] = arr[j];
            j--;
        }
        arr[j + 1] = key;
    }
}

void printArray(int arr[], int n) {
    for (int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

int main() {
    int arr[] = {12, 11, 13, 5, 6};
    int n = sizeof(arr) / sizeof(arr[0]);

    printf("Original Array:\n");
    printArray(arr, n);

    insertionSort(arr, n);

    printf("Sorted Array (Insertion Sort):\n");
    printArray(arr, n);

    return 0;
}

Sample Output

text (ISO Standard)
Copy
Original Array:
12 11 13 5 6 
Sorted Array (Insertion Sort):
5 6 11 12 13 

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Complexity Analysis

• Best Case Time: O(n) (When array is already sorted).
• Worst & Average Case Time: O(n²) (When sorted in reverse).
• Space Complexity: O(1) in-place auxiliary memory.
• Stability: Stable (preserves order of identical elements).

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Related Sorting Algorithms

• Compare with Selection Sort in C.
• Review array indexing in Arrays in C Programming.