chore(C): add shell sort (#678)

algorithms/C/README.md

@@ -51,6 +51,7 @@
 - [Heap Sort](sorting/heap-sort.c)
 - [Selection Sort](sorting/selection-sort.c)
 - [Quick Sort](sorting/quick-sort.c)
+- [Shell Sort](sorting/shell-sort.c)
 
 ## Strings
 

algorithms/C/sorting/shell-sort.c

@@ -0,0 +1,51 @@
+#include <stdio.h>
+
+// Shell Sort
+void ShellSort(int a[], int n)
+{
+    int i, j, k, temp;
+    // Rearrange elements at each n/2, n/4, n/8, ... intervals
+    for (i = n / 2; i > 0; i /= 2)
+    {
+        for (j = i; j < n; j++)
+        {
+            temp = a[j];
+            for (k = j; k >= i && a[k - i] > temp; k -= i)
+            {
+                a[k] = a[k - i];
+            }
+            a[k] = temp;
+        }
+    }
+}
+
+// Prints the array
+void printArray(int a[], int size)
+{
+    for (int i = 0; i < size; ++i)
+    {
+        printf("%d ", a[i]);
+    }
+}
+
+int main()
+{
+    int a[] = {64, 25, 12, 22, 11, 90};
+    int n = sizeof(a) / sizeof(a[0]);
+    printf("Array before sorting:\n");
+    printArray(a, n);
+    ShellSort(a, n);
+    printf("\nArray after sorting:\n");
+    printArray(a, n);
+    return 0;
+}
+
+/*
+Output:
+Array before sorting:
+64 25 12 22 11 90
+Array after sorting:
+11 12 22 25 64 90
+
+Time Complexity: O(n log n)
+*/