Implement permutation

src/dev/w1zzrd/math/Permutation.kt

@@ -0,0 +1,50 @@
+package dev.w1zzrd.math
+
+import kotlin.collections.ArrayList
+
+class Permutation {
+    private val orderedElements: CharArray
+    private val perms: List<CharArray>
+
+    constructor(vararg permutations: CharArray) {
+        orderedElements = permutations.map(CharArray::toSet).reduceRight{ it, acc -> acc.union(it) }.toCharArray()
+        perms = permutations.reversed()
+    }
+
+    constructor(transpositions: ArrayList<Pair<Char, Char>>) {
+        orderedElements = transpositions.map(Pair<Char, *>::first).union(transpositions.map(Pair<*, Char>::second)).toCharArray()
+        perms = transpositions.map { charArrayOf(it.first, it.second) }
+    }
+
+
+    /**
+     * Combine two permutations
+     */
+    operator fun times(perm: Permutation)
+            = Permutation(this(*perm(*orderedElements)).zip(orderedElements)    // Generate transpositions
+        .foldRight(ArrayList<Pair<Char, Char>>()){                              // Deduplicate transpositions
+                insert, acc ->
+            acc.firstOrNull {
+                (it.first == insert.first && it.second == insert.second) || (it.first == insert.second && it.second == insert.first)
+            } ?: acc.add(insert)
+            acc
+        })
+
+    operator fun times(perm: CharArray) = this * Permutation(perm)
+
+    operator fun invoke(vararg elements: Char): CharArray {
+        // Apply all permutations
+        for(perm in perms)
+            // Check each element-permutation
+            for(itemIndex in elements.indices)
+                // Check if permutation matches
+                for(index in perm.indices)
+                    // If permutation matches, apply it and go to next element
+                    if(elements[itemIndex] == perm[index]) {
+                        elements[itemIndex] = perm[(index + 1) % perm.size]
+                        break
+                    }
+
+        return elements
+    }
+}