Java Program for Binary Search (Recursive and Iterative)

Difficulty Level : Medium
Last Updated : 24 Sep, 2020

We basically ignore half of the elements just after one comparison.

Compare x with the middle element.
If x matches with the middle element, we return the mid index.
Else If x is greater than the mid element, then x can only lie in right half subarray after the mid element. So we recur for the right half.
Else (x is smaller) recur for the left half.

Java

// Java implementation of recursive Binary Search
class BinarySearch {
   
    // Returns index of x if it is present
    // in arr[l..r], else return -1
    int binarySearch(int arr[], int l,
                          int r, int x)
    {
        //Restrict the boundary of right index
        // and the left index to prevent
        // overflow of indices.
        if (r >= l && l<arr.length-1) {
           
            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[])
    {
        BinarySearch ob = new BinarySearch();
        int arr[] = { 2, 3, 4, 10, 40 };
        int n = arr.length;
        int x = 10;
        int result = ob.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 */

Output:

Element found at index 3

Java

// Java implementation of iterative Binary Search
class BinarySearch {
    // Returns index of x if it is present in arr[], else
    // return -1
    int binarySearch(int arr[], int x)
    {
        int l = 0, r = arr.length - 1;
        while (l <= r) {
            int m = l + (r - l) / 2;
 
            // Check if x is present at mid
            if (arr[m] == x)
                return m;
 
            // If x greater, ignore left half
            if (arr[m] < x)
                l = m + 1;
 
            // If x is smaller, ignore right half
            else
                r = m - 1;
        }
 
        // if we reach here, then element was not present
        return -1;
    }
 
    // Driver method to test above
    public static void main(String args[])
    {
        BinarySearch ob = new BinarySearch();
        int arr[] = { 2, 3, 4, 10, 40 };
        int n = arr.length;
        int x = 10;
        int result = ob.binarySearch(arr, x);
        if (result == -1)
            System.out.println("Element not present");
        else
            System.out.println("Element found at index " + result);
    }
}

Output:

Element found at index 3

Please refer complete article on Binary Search for more details!

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