Interpolation Search Program in C

Interpolation search is an improved variant of binary search. This search algorithm works on the probing position of the required value. For this algorithm to work properly, the data collection should be in sorted and equally distributed form.

It's runtime complexity is log₂(log₂ n).

Implementation in C

#include<stdio.h>

#define MAX 10

// array of items on which linear search will be conducted. 
int list[MAX] = { 10, 14, 19, 26, 27, 31, 33, 35, 42, 44 };

int find(int data) {
   int lo = 0;
   int hi = MAX - 1;
   int mid = -1;
   int comparisons = 1;      
   int index = -1;

   while(lo <= hi) {
      printf("\nComparison %d  \n" , comparisons ) ;
      printf("lo : %d, list[%d] = %d\n", lo, lo, list[lo]);
      printf("hi : %d, list[%d] = %d\n", hi, hi, list[hi]);
      
      comparisons++;

      // probe the mid point 
      mid = lo + (((double)(hi - lo) / (list[hi] - list[lo])) * (data - list[lo]));
      printf("mid = %d\n",mid);

      // data found 
      if(list[mid] == data) {
         index = mid;
         break;
      } else {
         if(list[mid] < data) {
            // if data is larger, data is in upper half 
            lo = mid + 1;
         } else {
            // if data is smaller, data is in lower half 
            hi = mid - 1;
         }
      }               
   }
   
   printf("\nTotal comparisons made: %d", --comparisons);
   return index;
}

int main() {
   //find location of 33
   int location = find(33);

   // if element was found 
   if(location != -1)
      printf("\nElement found at location: %d" ,(location+1));
   else
      printf("Element not found.");
   
   return 0;
}

If we compile and run the above program, it will produce the following result −

Output

Comparison 1
lo : 0, list[0] = 10
hi : 9, list[9] = 44
mid = 6

Total comparisons made: 1
Element found at location: 7

You can change the search value and execute the program to test it.