Project architecture and naive solver solution

Set up project architecture interfaces and add a naive implementation
of a solver in DumbBruteSolver

src/main/java/com/cleverthis/interview/DumbBruteSolver.java

@@ -0,0 +1,106 @@
+package com.cleverthis.interview;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Stream;
+
+/**
+ * Brute-forces padlock using lexicographically ordered permutation generation
+ *
+ * Algorithm documented at: https://en.wikipedia.org/wiki/Permutation#Generation_in_lexicographic_order
+ */
+public class DumbBruteSolver implements SolverInterface {
+
+    /**
+     * Solves the padlock passed in to the method. The padlock's internal state should be correct after this method
+     * runs.
+     * @param padlockAdapter A padlock conforming to the PadlockAdapter contract
+     */
+    @Override
+    public void solve(PadlockAdapter padlockAdapter) {
+        int numpadSize = padlockAdapter.getNumpadSize();
+
+        Integer[] currentPermutation = new Integer[numpadSize];
+        for(int i = 0; i < numpadSize; i++) {
+            currentPermutation[i] = i;
+        }
+
+        while(true) {
+            boolean isCorrect = checkPermutation(currentPermutation, padlockAdapter);
+
+            if (!isCorrect) {
+                boolean nextPermutationExists = calculateNextPermutation(currentPermutation, numpadSize);
+                if(!nextPermutationExists) {
+                    return;
+                }
+            } else {
+                return;
+            }
+        }
+
+    }
+
+    /**
+     * Writes the permutation to the padlock's memory and checks whether this permutation is the correct passcode.
+     * This is a naive solution that makes no considerations for write-cost.
+     * @param permutation The permutation to write to the padlock
+     * @param padlockAdapter The padlock to write to
+     * @return True if the correct padlock passcode has been found, false otherwise
+     */
+    protected boolean checkPermutation(Integer[] permutation, PadlockAdapter padlockAdapter) {
+        for(int i = 0; i < padlockAdapter.getNumpadSize(); i++) {
+            padlockAdapter.writeInputBuffer(i, permutation[i]);
+        }
+
+        return padlockAdapter.isPasscodeCorrect();
+    }
+
+    /**
+     * Calculates the next permutation in lexicographic order, based on the algorithm linked on wikipedia
+     * @param currentPermutation The current permutation to run the algorithm on
+     * @param numpadSize The number of items in the set to be permuted
+     * @return true if next permutation successfully generated, false if permutations have been exhausted
+     */
+    protected boolean calculateNextPermutation(Integer[] currentPermutation, int numpadSize) {
+        if(numpadSize < 2) { return false; }
+
+        //Integer k, l;
+
+        // Find the k and l indices, such that they meet the criteria for the permutation algorithm.
+        // If such indice values are found, swap them, then reverse the array subset from k+1 to the end of the array
+        for(int k = (numpadSize - 2); k >= 0; k--) {
+            if(currentPermutation[k] < currentPermutation[k + 1]) {
+
+                for(int l = (numpadSize - 1); l > k; l--) {
+                    if(currentPermutation[k] < currentPermutation[l]) {
+                        // Swap index k value and index l value in permutations array
+                        // TODO: Could be a better swap algorithm
+                        int tempInt = currentPermutation[k];
+                        currentPermutation[k] = currentPermutation[l];
+                        currentPermutation[l] = tempInt;
+
+                        // Split the currentPermutation array into two slices. The slice happens at index k, with index k
+                        // inclusive to the first slice
+                        Integer[] firstSlice = Arrays.stream(currentPermutation, 0, k + 1).toArray(Integer[]::new);
+                        Integer[] secondSlice = Arrays.stream(currentPermutation, k + 1, numpadSize).toArray(Integer[]::new);
+
+                        // Reverse the subset of the permutation array from index k+1 to the end of the array
+                        Collections.reverse(Arrays.asList(secondSlice));
+
+                        // Concat the non-reversed and reversed subarrays into a new permutation
+                        Integer[] newPermutation = Stream.concat(Arrays.stream(firstSlice), Arrays.stream(secondSlice)).toArray(Integer[]::new);
+
+                        // Copy the new permutation into currentPermutation to return it
+                        System.arraycopy(newPermutation, 0, currentPermutation, 0, numpadSize);
+
+                        return true;
+                    }
+                }
+            }
+        }
+
+        return false;
+    }
+}