added iterative algorithm for binary_search

searching/binary_search.c

@@ -3,6 +3,9 @@
  * @brief Program to perform [binary
  * search](https://en.wikipedia.org/wiki/Binary_search_algorithm) of a target
  * value in a given *sorted* array.
+ * @authors [James McDermott](https://github.com/theycallmemac) - recursive
+ * algorithm
+ * @authors [Krishna Vedala](https://github.com/kvedala) - iterative algorithm
  */
 #include <assert.h>
 #include <stdio.h>
@@ -15,7 +18,7 @@
  * \returns location of x assuming array arr[l..r] is present
  * \returns -1 otherwise
  */
-int binarysearch(const int *arr, int l, int r, int x)
+int binarysearch1(const int *arr, int l, int r, int x)
 {
     if (r >= l)
     {
@@ -27,16 +30,47 @@ int binarysearch(const int *arr, int l, int r, int x)
 
         // If element is smaller than middle
         if (arr[mid] > x)
-            return binarysearch(arr, l, mid - 1, x);
+            return binarysearch1(arr, l, mid - 1, x);
 
         // Else element is in right subarray
-        return binarysearch(arr, mid + 1, r, x);
+        return binarysearch1(arr, mid + 1, r, x);
     }
 
     // When element is not present in array
     return -1;
 }
 
+/** Iterative implementation
+ * \param[in] arr array to search
+ * \param l left index of search range
+ * \param r right index of search range
+ * \param x target value to search for
+ * \returns location of x assuming array arr[l..r] is present
+ * \returns -1 otherwise
+ */
+int binarysearch2(const int *arr, int l, int r, int x)
+{
+    int mid = l + (r - l) / 2;
+
+    while (arr[mid] != x)
+    {
+        if (r <= l || r < 0)
+            return -1;
+
+        if (arr[mid] > x)
+            // If element is smaller than middle
+            r = mid - 1;
+        else
+            // Else element is in right subarray
+            l = mid + 1;
+
+        mid = l + (r - l) / 2;
+    }
+
+    // When element is not present in array
+    return mid;
+}
+
 /** Test implementations */
 void test()
 {
@@ -49,16 +83,22 @@ void test()
     // set value to look for
     int x = 10;
     // set result to what is returned from binarysearch
-    int result = binarysearch(arr, 0, n - 1, x);
+    int result = binarysearch1(arr, 0, n - 1, x);
     assert(result == 3);
-    printf("passed\n");
+    printf("passed recursive... ");
+    result = binarysearch2(arr, 0, n - 1, x);
+    assert(result == 3);
+    printf("passed iterative...\n");
 
     printf("Test 2.... ");
     x = 5;
     // set result to what is returned from binarysearch
-    result = binarysearch(arr, 0, n - 1, x);
+    result = binarysearch1(arr, 0, n - 1, x);
     assert(result == -1);
-    printf("passed\n");
+    printf("passed recursive... ");
+    result = binarysearch2(arr, 0, n - 1, x);
+    assert(result == -1);
+    printf("passed iterative...\n");
 }
 
 /** Main function */