## This Week in Dev

### Java, Unit Tests, CodeSignal

Up to level 40 this week on CodeSignal.com - that’s over 100 challenges solved in just a couple weeks

## Evaluating Efficiency with Big-O Notation

Check out my recursive solution to this arcade problem, which made it possible for me solve a problem in *constant time* O(1), a whole world of improvement over my previous approach, which turned out to be a *factorial time* O(n!) solution. Big-O notation is a means of evaluating the computational efficiency of different algorithms.

My solution

boolean stringsRearrangement(String[] inputArray) {
String[] sorted = Arrays.stream(inputArray).sorted().toArray(String[]::new);

// test input that does not include duplicates
if (inputArray.length == Arrays.stream(inputArray).distinct().count()
&& allStringsConform(sorted)) return true;

// test starting with each individual input string
for (String string : Arrays.stream(sorted).distinct().toArray(String[]::new)) {
ArrayDeque<String> input = new ArrayDeque<>(Arrays.stream(sorted).collect(Collectors.toList()));
input.remove(string);
ArrayDeque<String> output = new ArrayDeque<>(Collections.singletonList(string));
if (testPermutations(input, output)) return true;
}

return false;
}


## This Week in Dev

### Java, Streams and Loops - Affine Cipher

import java.math.BigInteger;

class AffineCipher {

private static final int M = 26;        // size of alphabet
private static final int A = (int) 'a'; // zero-index of 'a' (ASCII code point 97)

String encode(String input, int a, int b) {
if (greatestCommonDivisor(a, M) != 1) {
throw new IllegalArgumentException("Error: keyA and alphabet size must be coprime.");
}

StringBuilder output = new StringBuilder();

for (int codePoint :
input.replaceAll("\\W", "") // nix punctuation and whitespace
.toLowerCase()
.toCharArray()
) {
output.append( Character.isDigit(codePoint)
? (char) codePoint
: (char) (((a * (codePoint - A) + b) % M) + A));
}

return String.join(" ", splitString(output.toString(), 5));
}