Insertion Sort

Build the sorted prefix one item at a time, shifting larger values right until the current key can be inserted.

Algorithm

The checked-in replay follows the same small input and final output across all 21 DSA books, so this C DSA implementation can be compared directly with the other languages.

Basic Implementation

basic.c

#include <stdio.h>

int main(void) {
    int arr[] = {5, 1, 4, 2, 8};
    int n = 5;
    for (int i = 1; i < n; ++i) {
        int key = arr[i];
        int j = i - 1;
        while (j >= 0 && arr[j] > key) {
            arr[j + 1] = arr[j];
            j--;
        }
        arr[j + 1] = key;
    }
    printf("[");
    for (int i = 0; i < n; ++i) {
        if (i > 0) printf(", ");
        printf("%d", arr[i]);
    }
    printf("]\n");
    return 0;
}

Complexity

Time: O(n^2) worst and average, O(n) best
Space: O(1)
Stable: yes

Implementation notes

Keep the explicit algorithmic steps instead of calling a standard-library sort. The replay is meant to expose comparisons, movement, and recursion.
The implementation is intentionally compact for learning and replay, not a production sorting utility.

sorted prefix Positions before the scan index are already sorted.

shifting Larger values move one slot right to make room for the key.