Author: Luca Zanini

  • Truncatable primes

    —

    by

    Luca Zanini
    in

    Project Euler Problem 37: The number 3797 has an interesting property. Being prime itself, it is possible to continuously remove digits from left to right, and remain prime at each stage: 3797, 797, 97, and 7. Similarly we can work from right to left: 3797, 379, 37, and 3. Find the sum of the only…

  • Double-base palindromes

    —

    by

    Luca Zanini
    in

    From the Project Euler Problem 36: The decimal number, 585 = 10010010012 (binary), is palindromic in both bases. Find the sum of all numbers, less than one million, which are palindromic in base 10 and base 2. (Please note that the palindromic number, in either base, may not include leading zeros.) checked

  • How to implement Up Navigation

    —

    by

    Luca Zanini
    in

    In this example you can see how to implement the Up Navigation, i.e. the option to go back to a previous activity using the button in the upper left of the action bar. The previous activity can be a fixed activity or an activity determined at runtime.

  • Circular primes

    —

    by

    Luca Zanini
    in

    From the Project Euler Problem 35: The number, 197, is called a circular prime because all rotations of the digits: 197, 971, and 719, are themselves prime. There are thirteen such primes below 100: 2, 3, 5, 7, 11, 13, 17, 31, 37, 71, 73, 79, and 97. How many circular primes are there below…

  • Digit factorials

    —

    by

    Luca Zanini
    in

    From the Project Euler Problem 34: 145 is a curious number, as 1! + 4! + 5! = 1 + 24 + 120 = 145. Find the sum of all numbers which are equal to the sum of the factorial of their digits. Note: as 1! = 1 and 2! = 2 are not sums…

  • Replacing a Fragment in a Tab Layout with an ActionBar

    —

    by

    Luca Zanini
    in

    In the post Tab Layout in Android with ActionBar and Fragment the fragments can’t be replaced later, in this post I write the changes in order to replace the first fragment of the first tab with a third fragment using a button at runtime.

  • Digit canceling fractions

    —

    by

    Luca Zanini
    in

    From the Project Euler Problem 33: The fraction 49/98 is a curious fraction, as an inexperienced mathematician in attempting to simplify it may incorrectly believe that 49/98 = 4/8, which is correct, is obtained by cancelling the 9s. We shall consider fractions like, 30/50 = 3/5, to be trivial examples. There are exactly four non-trivial…

  • The services in Android

    —

    by

    Luca Zanini
    in

    A service is a task running in the background to perform actions without a user interface and they are used to perform long running operations with a significant use of resources by avoiding delays in the user experience. The services belong to one or both of the following categories: started: the service is launched using…

  • Passing an object from an Activity to another

    —

    by

    Luca Zanini
    in

    The method startActivity(Intent intent) of the class Activity allows you to call a second activity specified using the argument Intent. You can associate primitive data or primitive data array to the argument Intent and then the second Activity can access them, you can also pass objects of type String using methods of the class Bundle…

  • Pandigital products

    —

    by

    Luca Zanini
    in

    From the Project Euler Problem 32: We shall say that an n-digit number is pandigital if it makes use of all the digits 1 to n exactly once; for example, the 5-digit number, 15234, is 1 through 5 pandigital. The product 7254 is unusual, as the identity, 39 × 186 = 7254, containing multiplicand, multiplier,…