Modify interpolation search

searching/interpolation_search.c

@@ -1,35 +1,53 @@
 #include<stdio.h>
-int interpolationSearch(int arr[], int n, int x)
-{ 
-    int q=NULL;
-    while(q<n)
-    {
-     if(arr[q]==x)
-     return q;
-     q++;
+
+/* By comparison, binary search always chooses the middle of the remaining
+ * search space, discarding one half or the other, depending on the comparison
+ * between the key found at the estimated position and the key sought. The remaining
+ * search space is reduced to the part before or after the estimated position.
+ * The linear search uses equality only as it compares elements one-by-one from the start, ignoring any sorting.
+ * On average the interpolation search makes about log(log(n)) comparisons (if the elements
+ * are uniformly distributed), where n is the number of elements to be searched. In the worst case
+ * (for instance where the numerical values of the keys increase exponentially) it can make up to O(n) comparisons.
+ * In interpolation-sequential search, interpolation is used to find an item near the one being searched for,
+ * then linear search is used to find the exact item. */
+
+int interpolationSearch(int arr[], int n, int key)
+{
+    int low = 0, high = n - 1;
+    while (low <= high && key >= arr[low] && key <= arr[high]) {
+        /* Calculate the nearest posible position of key */
+        int pos = low + ((key - arr[low]) * (high - low)) / (arr[high] - arr[low]);
+        if (key > arr[pos])
+            low = pos + 1;
+        else if (key < arr[pos])
+            high = pos - 1;
+        else /* Found */
+            return pos;
     }
+    /* Not found */
     return -1;
 }
- 
+
 
 int main()
 {
-    // Array of items on which search will
-    // be conducted.
     int x;
     int arr[] =  {10, 12, 13, 16, 18, 19, 20, 21, 22, 23,
                   24, 33, 35, 42, 47};
-    int n = sizeof(arr)/sizeof(arr[0]); //To get length of an array
-
-    printf("Enter the no, to be searched");
-    scanf("%d",&x); // Element to be searched
-
+    int n = sizeof(arr)/sizeof(arr[0]);
+
+    printf("Array: ");
+    for(int i = 0; i < n; i++)
+        printf("%d ", arr[i]);
+    printf("\nEnter the number to be searched: ");
+    scanf("%d",&x); /* Element to be searched */
+
     int index = interpolationSearch(arr, n, x);
- 
-    // If element was found
+
+    /* If element was found */
     if (index != -1)
-        printf("Element found at position %d", index+1);
+        printf("Element found at position: %d\n", index);
     else
-        printf("Element not found.");
+        printf("Element not found.\n");
     return 0;
 }