Permutations

Author: forketyfork

src/main/kotlin/com/forketyfork/codingproblems/Permutations.kt

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+package com.forketyfork.codingproblems
+
+import java.util.*
+
+/**
+ * Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order.
+ *
+ * @see "Daily Coding Problem #1128"
+ * @see <a href="https://leetcode.com/problems/permutations/description/">LeetCode #46. Permutations</a>
+ */
+class Permutations {
+
+ fun permute(nums: IntArray): List<List<Int>> = permute(LinkedList(nums.toList()))
+
+ private fun permute(nums: LinkedList<Int>): List<MutableList<Int>> {
+ if (nums.isEmpty()) {
+ return listOf(mutableListOf())
+ }
+ return nums.indices.flatMap { idx ->
+ nums.removeAt(idx).let { el ->
+ permute(nums).also { lists ->
+ lists.forEach { it.add(el) }
+ nums.add(idx, el)
+ }
+ }
+ }
+ }
+
+}

src/test/kotlin/com/forketyfork/codingproblems/PermutationsTest.kt

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+package com.forketyfork.codingproblems
+
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.params.ParameterizedTest
+import org.junit.jupiter.params.provider.Arguments.of
+import org.junit.jupiter.params.provider.MethodSource
+
+class PermutationsTest {
+ companion object {
+ @JvmStatic
+ fun data() = arrayOf(
+ of(
+ intArrayOf(1, 2, 3),
+ listOf(
+ listOf(1, 2, 3),
+ listOf(1, 3, 2),
+ listOf(2, 1, 3),
+ listOf(2, 3, 1),
+ listOf(3, 1, 2),
+ listOf(3, 2, 1)
+ )
+ ),
+ of(
+ intArrayOf(0, 1),
+ listOf(listOf(0, 1), listOf(1, 0))
+ ),
+ of(
+ intArrayOf(1),
+ listOf(listOf(1))
+ ),
+ )
+ }
+
+ @ParameterizedTest(name = "input {0}, expected {1}")
+ @MethodSource("data")
+ fun test(input: IntArray, expected: List<List<Int>>) {
+ assertThat(Permutations().permute(input)).containsExactlyInAnyOrderElementsOf(expected)
+ }
+
+}