Exponential Search.c

algorithms/searching/Exponential Search.c

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+#include <stdio.h>
+#include <time.h>
+#include <math.h>
+#define min
+
+int binarySearch(int arr[], int, int, int);
+
+// Returns position of first occurrence of
+// x in array
+int exponentialSearch(int arr[], int n, int x)
+{
+    // If x is present at first location itself
+    if (arr[0] == x)
+        return 0;
+
+    // Find range for binary search by
+    // repeated doubling
+    int i = 1;
+    while (i < n && arr[i] <= x)
+        i = i*2;
+
+    //  Call binary search for the found range.
+    return binarySearch(arr, i/2, 
+                            min(i, n-1), x);
+}
+
+// A recursive binary search function. It returns
+// location of x in  given array arr[l..r] is
+// present, otherwise -1
+int binarySearch(int arr[], int l, int r, int x)
+{
+    if (r >= l)
+    {
+        int mid = l + (r - l)/2;
+
+        // If the element is present at the middle
+        // itself
+        if (arr[mid] == x)
+            return mid;
+
+        // If element is smaller than mid, then it
+        // can only be present n left subarray
+        if (arr[mid] > x)
+            return binarySearch(arr, l, mid-1, x);
+
+        // Else the element can only be present
+        // in right subarray
+        return binarySearch(arr, mid+1, r, x);
+    }
+
+    // We reach here when element is not present
+    // in array
+    return -1;
+}
+
+// Driver code
+int main(void)
+{
+   int arr[] = {2, 3, 4, 10, 40};
+   int n = sizeof(arr)/ sizeof(arr[0]);
+   int x = 10;
+   int result = exponentialSearch(arr, n, x);
+   (result == -1)? printf("Element is not 
+                            present in array")
+                 : printf("Element is present 
+                                 at index %d",
+                                       result);
+   return 0;
+}