Added Exponential Search in PHP (jainaman224#2957)

Update Exponential_Search.php

Author: thakran14

Exponential_Search/Exponential_Search.php

@@ -0,0 +1,50 @@
+<?php 
+// Exponential search in PHP
+
+function Binary_Search($input_arr, $left, $right, $x)
+{
+    if ($right > $left) 
+    {
+        $mid = $left + ($right - $left) / 2; 
+        if ($input_arr[$mid] == $x) 
+            return $mid; 
+        if ($x < $input_arr[$mid] ) 
+            return Binary_Search($input_arr, $left, $mid - 1, $x); 
+		
+        return Binary_Search($input_arr, $mid + 1, $right, $x); 
+    }
+    return -1; 
+}
+
+function Exponential_Search($input_arr,$size,$x)
+{
+	if ($input_arr[0] == $x)
+        return 0;
+    $i = 1;
+	while ($i < $size and $input_arr[$i] <= $x)
+    {
+	    $i = $i * 2;
+	}
+	
+	return Binary_Search($input_arr, $i / 2, min($i, $size), $x);
+	
+}
+
+//Driver Code
+
+$input_arr = array(1, 2, 3, 4, 5, 6);
+$size = count($input_arr); 
+$x = 4;
+$result = exponential_search($input_arr, $size, $x);
+if ($result != -1)
+    echo "The index at which the element " , $x,  " is present is " , $result;
+    
+else
+    echo "The element is not present in array";
+
+/*
+OUTPUT:
+The index at which the element 4 is present is 3
+*/
+
+?>