Category: Uncategorized
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Preference element in xml and the click event
If you have an EditTextPreference tag in a xml file you can catch the click event implementing OnSharedPreferenceChangeListener but it doesn’t work if you have a Preference tag in the xml file. Consider the following code inside a xml file for the preferences: <Preference android:key=”my_key” android:summary=”my_summary” android:title=”my_title” > </Preference>
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Number spiral diagonals
From the Project Euler Problem 28: Starting with the number 1 and moving to the right in a clockwise direction a 5 by 5 spiral is formed as follows: 21 22 23 24 25 20 7 8 9 10 19 6 1 2 11 18 5 4 3 12 17 16 15 14 13 It…
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Quadratic primes
From the Project Euler Problem 27: Euler discovered the remarkable quadratic formula: n² + n + 41 It turns out that the formula will produce 40 primes for the consecutive values n = 0 to 39. However, when n = 40, 40² + 40 + 41 = 40(40 + 1) + 41 is divisible by…
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Reciprocal cycles
From the Project Euler Problem 26: A unit fraction contains 1 in the numerator. The decimal representation of the unit fractions with denominators 2 to 10 are given: 1/2 = 0.5 1/3 = 0.(3) 1/4 = 0.25 1/5 = 0.2 1/6 = 0.1(6) 1/7 = 0.(142857) 1/8 = 0.125 1/9 = 0.(1) 1/10 = 0.1…
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1000-digit Fibonacci number
From the Project Euler Problem 25: The Fibonacci sequence is defined by the recurrence relation: Fn = Fn−1 + Fn−2, where F1 = 1 and F2 = 1. Hence the first 12 terms will be: F1 = 1 F2 = 1 F3 = 2 F4 = 3 F5 = 5 F6 = 8 F7 =…
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Lexicographic permutations
From the Project Euler Problem 24: A permutation is an ordered arrangement of objects. For example, 3124 is one possible permutation of the digits 1, 2, 3 and 4. If all of the permutations are listed numerically or alphabetically, we call it lexicographic order. The lexicographic permutations of 0, 1 and 2 are: 012 021…
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Non-abundant sums
From the Project Euler Problem 23: A perfect number is a number for which the sum of its proper divisors is exactly equal to the number. For example, the sum of the proper divisors of 28 would be 1 + 2 + 4 + 7 + 14 = 28, which means that 28 is a…
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ìNames scores
From the Project Euler Problem 22: Using […] a 46K text file containing over five-thousand first names, begin by sorting it into alphabetical order. Then working out the alphabetical value for each name, multiply this value by its alphabetical position in the list to obtain a name score. For example, when the list is sorted…
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Amicable numbers
From the Project Euler Problem 21: Let d(n) be defined as the sum of proper divisors of n (numbers less than n which divide evenly into n). If d(a) = b and d(b) = a, where a ≠ b, then a and b are an amicable pair and each of a and b are called…
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Factorial digit sum
From the Project Euler Problem 20: n! means n * (n – 1) * … * 3 * 2 * 1 For example, 10! = 10 * 9 … * 3 * 2 * 1 = 3628800, and the sum of the digits in the number 10! is 3 + 6 + 2 + 8…