adds example code for binary search in ch 13

Author: ARajan1084

src/com/codefortomorrow/advanced/chapter13/examples/BinarySearch.java

@@ -0,0 +1,47 @@
+package com.codefortomorrow.advanced.chapter13.examples;
+
+public class BinarySearch {
+        // Java implementation of recursive Binary Search
+        // Returns index of x if it is present in arr[l..
+        // r], else return -1
+        public static 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 in 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 method to test above
+        public static void main(String args[])
+        {
+            int arr[] = { 2, 3, 4, 10, 40 };
+            int n = arr.length;
+            int x = 10;
+            int result = binarySearch(arr, 0, n - 1, x);
+            if (result == -1)
+                System.out.println("Element not present");
+            else
+                System.out.println("Element found at index " + result);
+        }
+    /* This code is contributed by Rajat Mishra
+    https://www.geeksforgeeks.org/binary-search/ */
+
+}