chore: split solutions by language

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/kt/binary-tree-inorder-traversal.kt

@@ -0,0 +1,26 @@
+/**
+ * Example:
+ * var ti = TreeNode(5)
+ * var v = ti.`val`
+ * Definition for a binary tree node.
+ * class TreeNode(var `val`: Int) {
+ *     var left: TreeNode? = null
+ *     var right: TreeNode? = null
+ * }
+ */
+class Solution {
+    fun inorderTraversal(root: TreeNode?, values: MutableList<Int>): List<Int> {
+        if (root == null) {
+            return values
+        }
+
+        inorderTraversal(root.left, values)
+        values.add(root.`val`!!)
+        inorderTraversal(root.right, values)
+
+        return values
+    }
+
+    fun inorderTraversal(root: TreeNode?): List<Int>
+        = inorderTraversal(root, mutableListOf<Int>())
+}

problems/kt/binary-tree-level-order-traversal.kt

@@ -0,0 +1,27 @@
+/**
+ * Example:
+ * var ti = TreeNode(5)
+ * var v = ti.`val`
+ * Definition for a binary tree node.
+ * class TreeNode(var `val`: Int) {
+ *     var left: TreeNode? = null
+ *     var right: TreeNode? = null
+ * }
+ */
+class Solution {
+    private fun levelOrder(root: TreeNode?, levels: MutableList<MutableList<Int>>, level: Int): MutableList<MutableList<Int>> {
+        if (root == null) {
+            return levels
+        }
+
+        if (level + 1 > levels.size) {
+            levels.add(mutableListOf<Int>())
+        }
+
+        levels[level].add(root.`val`)
+        levelOrder(root.left, levels, level + 1)
+        return levelOrder(root.right, levels, level + 1)
+    }
+
+    fun levelOrder(root: TreeNode?): List<List<Int>> = levelOrder(root, mutableListOf<MutableList<Int>>(), 0)
+}

problems/kt/check-if-every-row-and-column-contains-all-numbers.kt

@@ -0,0 +1,13 @@
+class Solution {
+    fun checkValid(matrix: Array<IntArray>): Boolean {
+        val n = matrix.size
+        val required = (1..n).toSet()
+
+        fun checkDimension(
+            dimensions: Iterable<Iterable<Int>>
+        ): Boolean = dimensions.all { it.toSet() == required }
+
+        return checkDimension(matrix.map(IntArray::toList)) &&
+            checkDimension((0 until n).map { x -> matrix.map { row -> row[x] }})
+    }
+}

problems/kt/construct-string-from-binary-tree.kt

@@ -0,0 +1,30 @@
+/**
+ * Example:
+ * var ti = TreeNode(5)
+ * var v = ti.`val`
+ * Definition for a binary tree node.
+ * class TreeNode(var `val`: Int) {
+ *     var left: TreeNode? = null
+ *     var right: TreeNode? = null
+ * }
+ */
+class Solution {
+    fun tree2str(root: TreeNode?): String {
+        if (root == null) {
+            return ""
+        }
+
+        val value = root.`val`.toString()
+        val left = "(${tree2str(root.left)})"
+        val right = "(${tree2str(root.right)})"
+
+
+        if (left == "()" && right == "()") {
+            return value
+        } else if (right == "()") {
+            return "$value$left"
+        }
+
+        return "$value$left$right"
+    }
+}

problems/kt/first-unique-character-in-a-string.kt

@@ -0,0 +1,26 @@
+class Solution {
+    private data class Accumulator(val firstIndex: Int, var count: Int = 0) {
+        fun add() {
+            count++
+        }
+    }
+
+    fun firstUniqChar(s: String): Int = s
+        .foldIndexed(mutableMapOf<Char, Accumulator>()) { i, acc, c ->
+            acc.getOrPut(c) { Accumulator(i) }.add()
+            acc
+        }
+        .filterValues { it.count == 1 }
+        .minByOrNull { (_, acc) -> acc.firstIndex }
+        ?.value
+        ?.firstIndex
+        ?: -1
+}
+
+fun main() {
+    val s = Solution()
+
+    check(s.firstUniqChar("leetcode") == 0)
+    check(s.firstUniqChar("loveleetcode") == 2)
+    check(s.firstUniqChar("aabb") == -1)
+}

problems/kt/iterator-for-combination.kt

@@ -0,0 +1,46 @@
+class CombinationIterator(val characters: String, val combinationLength: Int) {
+    private var indices = (0 until combinationLength).toMutableList()
+
+    private fun nextCombination(index: Int) {
+        // bump the current index
+        indices[index]++
+
+        // we have gone through the whole string
+        while (indices[index] == characters.length && index > 0) {
+            // bump the previous index
+            nextCombination(index - 1)
+
+            // set current index to previous + 1, since it must be the following one
+            indices[index] = indices[index - 1] + 1
+        }
+    }
+
+    // By default bumping just the last index
+    private fun nextCombination() = nextCombination(combinationLength - 1)
+
+    private fun getCombination(): String =
+        indices.map { characters[it] }.joinToString(separator="")
+
+    fun next(): String {
+        // construct the combination
+        val combination = getCombination()
+
+        // bump the combination
+        nextCombination()
+
+        return combination
+    }
+
+    fun hasNext(): Boolean =
+        indices.all {
+            it < characters.length
+        }
+
+}
+
+/**
+ * Your CombinationIterator object will be instantiated and called as such:
+ * var obj = CombinationIterator(characters, combinationLength)
+ * var param_1 = obj.next()
+ * var param_2 = obj.hasNext()
+ */

problems/kt/lowest-common-ancestor-of-a-binary-search-tree.kt

@@ -0,0 +1,37 @@
+/**
+ * Definition for a binary tree node.
+ * class TreeNode(var `val`: Int = 0) {
+ *     var left: TreeNode? = null
+ *     var right: TreeNode? = null
+ * }
+ */
+
+class Solution {
+    fun lowestCommonAncestor(root: TreeNode?, p: TreeNode?, q: TreeNode?): TreeNode? {
+        var ancestor: TreeNode? = null
+        var pTrack = root
+        var qTrack = root
+
+        while (pTrack == qTrack && pTrack != null && qTrack != null) {
+            ancestor = pTrack
+
+            if (pTrack!!.`val` == p!!.`val`) {
+                return p
+            } else if (p!!.`val` < pTrack!!.`val`) {
+                pTrack = pTrack.left
+            } else {
+                pTrack = pTrack.right
+            }
+
+            if (qTrack!!.`val` == q!!.`val`) {
+                return q
+            } else if (q!!.`val` < qTrack!!.`val`) {
+                qTrack = qTrack.left
+            } else {
+                qTrack = qTrack.right
+            }
+        }
+
+        return ancestor
+    }
+}

problems/kt/max-area-of-island.kt

@@ -0,0 +1,39 @@
+fun <A, B> product(xs: Sequence<A>, ys: Sequence<B>): Sequence<Pair<A, B>> =
+    xs.flatMap { x -> ys.map { y -> x to y } }
+
+fun <A, B> product(xs: Iterable<A>, ys: Iterable<B>): Sequence<Pair<A, B>> =
+    product(xs.asSequence(), ys.asSequence())
+
+class Solution {
+    fun BFS(grid: Array<IntArray>, coords: Pair<Int, Int>): Int {
+        val queue = ArrayDeque<Pair<Int, Int>>()
+        queue.addLast(coords)
+
+        var size = 0
+        while (!queue.isEmpty()) {
+            val (y, x) = queue.removeFirst()
+            if (grid[y][x] != 1) {
+                continue
+            }
+
+            for ((dy, dx) in sequenceOf(0 to 1, 1 to 0, 0 to -1, -1 to 0)) {
+                if (!(y + dy in grid.indices) || !(x + dx in grid[y + dy].indices)) {
+                    continue
+                } else if (grid[y + dy][x + dx] != 1) {
+                    continue
+                }
+
+                queue.addLast(y + dy to x + dx)
+            }
+
+            // mark it as done
+            grid[y][x] = 0
+            size++
+        }
+
+        return size
+    }
+
+    fun maxAreaOfIsland(grid: Array<IntArray>): Int =
+        product(grid.indices, grid.first().indices).map { BFS(grid, it) }.max() ?: 0
+}

problems/kt/maximize-distance-to-closest-person.kt

@@ -0,0 +1,18 @@
+class Solution {
+    private fun mapSeats(seats: IntArray): MutableList<Int> =
+        seats.map { if (it == 1) 0 else Int.MAX_VALUE }.toMutableList()
+
+    fun maxDistToClosest(seats: IntArray): Int {
+        val left: MutableList<Int> = mapSeats(seats)
+        for (i in left.indices.drop(1).filter { left[it] != 0 }) {
+            left[i] = left[i - 1] + 1
+        }
+
+        val right: MutableList<Int> = mapSeats(seats)
+        for (i in right.indices.reversed().drop(1).filter { right[it] != 0 }) {
+            right[i] = right[i + 1] + 1
+        }
+
+        return left.zip(right).map { (l, r) -> if (l < r) l else r }.max()!!
+    }
+}

problems/kt/maximum-units-on-a-truck.kt

@@ -0,0 +1,19 @@
+class Solution {
+    data class BoxType(val boxes: Int, val units: Int)
+    fun toBoxType(x: IntArray): BoxType = BoxType(x[0], x[1])
+
+    fun maximumUnits(boxTypes: Array<IntArray>, truckSize: Int): Int =
+        boxTypes
+        .map { toBoxType(it) }
+        .sortedByDescending(BoxType::units)
+        .fold(0 to 0) { acc, boxType ->
+            if (acc.first < truckSize) {
+                val count = minOf(truckSize - acc.first, boxType.boxes)
+
+                (acc.first + count) to (acc.second + count * boxType.units)
+            } else {
+                acc
+            }
+        }
+        .second
+}

problems/kt/minimum-number-of-refueling-stops.kt

@@ -0,0 +1,59 @@
+import java.util.PriorityQueue
+
+class Solution {
+    fun minRefuelStops(target: Int, startFuel: Int, stations: Array<IntArray>): Int {
+        var maxReach = startFuel
+        val availableRefuelling = PriorityQueue<Int>(reverseOrder())
+
+        var refuelled = 0
+        var i = 0
+
+        while (maxReach < target) {
+            while (i < stations.size && stations[i][0] <= maxReach) {
+                // keep track of possible refuels
+                availableRefuelling.add(stations[i][1])
+                i++
+            }
+
+            if (availableRefuelling.isEmpty()) {
+                // no refuels are available and target has not been reached
+                return -1
+            }
+
+
+            // refuel at least once in order to progress
+            maxReach += availableRefuelling.poll()!!
+            refuelled++
+        }
+        return refuelled
+    }
+}
+
+fun main() {
+    val s = Solution()
+
+    check(s.minRefuelStops(1, 1, arrayOf()) == 0)
+    check(s.minRefuelStops(100, 1, arrayOf(intArrayOf(10, 100))) == -1)
+    check(
+        s.minRefuelStops(
+            100, 10, arrayOf(intArrayOf(10, 60), intArrayOf(20, 30), intArrayOf(30, 30), intArrayOf(60, 40))
+        ) == 2
+    )
+    check(
+        s.minRefuelStops(
+            1000, 299,
+            arrayOf(
+                intArrayOf(13, 21),
+                intArrayOf(26, 115),
+                intArrayOf(100, 47),
+                intArrayOf(225, 99),
+                intArrayOf(299, 141),
+                intArrayOf(444, 198),
+                intArrayOf(608, 190),
+                intArrayOf(636, 157),
+                intArrayOf(647, 255),
+                intArrayOf(841, 123)
+            )
+        ) == 4
+    )
+}

problems/kt/power-of-three.kt

@@ -0,0 +1,13 @@
+class Solution {
+    fun isPowerOfThree(n: Int): Boolean {
+        if (n < 1) {
+            return false
+        }
+
+        var x = n
+        while (x % 3 == 0) {
+            x /= 3
+        }
+        return x == 1
+    }
+}

problems/kt/roman-to-integer.kt

@@ -0,0 +1,62 @@
+class Solution {
+    /**
+     * Holds fixed mapping of roman numerals to their respective numeric value.
+     */
+    private val values = mapOf(
+        'I' to 1, 'V' to 5, 'X' to 10, 'L' to 50, 'C' to 100, 'D' to 500, 'M' to 1000
+    )
+
+    /**
+     * Represents an accumulator for right fold when turning roman numeral into an integer value.
+     * @property sum Holds the current sum of the accumulator.
+     * @property next Holds the value of the previous roman numeral digit.
+     */
+    private data class Accumulator(val sum: Int = 0, val next: Int = 0) {
+        /**
+         * @param it Current roman numeral digit.
+         * @return Sign that is to be used when modifying sum of the accumulator.
+         */
+        private fun sign(it: Int): Int = when (next > it) {
+            true -> -1
+            false -> 1
+        }
+
+        /**
+         * @param it Currently processed roman numeral digit.
+         * @return Correctly updated accumulator.
+         */
+        fun update(it: Int): Accumulator = copy(sum = sum + sign(it) * it, next = it)
+    }
+
+    fun romanToInt(s: String): Int = s
+        .map { values[it]!! }
+        .foldRight(Accumulator()) { it, acc ->
+            acc.update(it)
+        }
+        .sum
+}
+
+fun main() {
+    val s = Solution()
+
+    val tests = mapOf(
+        "I" to 1,
+        "II" to 2,
+        "III" to 3,
+        "IV" to 4,
+        "V" to 5,
+        "VI" to 6,
+        "VII" to 7,
+        "VIII" to 8,
+        "IX" to 9,
+        "X" to 10,
+        "LVIII" to 58,
+        "MCMXCIV" to 1994
+    )
+
+    tests.forEach { (num, i) ->
+        check(s.romanToInt(num) == i) {
+            "$num: ${s.romanToInt(num)} == $i"
+        }
+    }
+}

problems/kt/split-array-into-consecutive-subsequences.kt

@@ -0,0 +1,37 @@
+class Solution {
+    private fun getFrequencies(nums: IntArray): MutableMap<Int, Int> {
+        val freqs = mutableMapOf<Int, Int>()
+
+        nums.forEach {
+            freqs[it] = 1 + freqs.getOrDefault(it, 0)
+        }
+
+        return freqs
+    }
+
+    fun isPossible(nums: IntArray): Boolean {
+        val frequencies = getFrequencies(nums)
+        val sortedNumbers = frequencies.keys.toList().sorted()
+
+        sortedNumbers.forEach {
+            while (frequencies[it]!! > 0) {
+                var last = 0
+                var j = it
+                var k = 0
+
+                while (frequencies.getOrDefault(j, 0) >= last) {
+                    last = frequencies[j]!!
+                    frequencies[j] = frequencies[j]!! - 1
+
+                    j++
+                    k++
+                }
+                if (k < 3) {
+                    return false
+                }
+            }
+        }
+
+        return true
+    }
+}

problems/kt/substring-with-concatenation-of-all-words.kt

@@ -0,0 +1,29 @@
+class Solution {
+    private fun buildTable(words: Sequence<String>): Map<String, Int> {
+        val table = mutableMapOf<String, Int>()
+
+        words.forEach {
+            table.put(it, 1 + table.getOrElse(it) { 0 })
+        }
+
+        return table
+    }
+    private fun buildTable(s: String, length: Int): Map<String, Int> =
+        buildTable(s.chunked(length).asSequence())
+
+    fun findSubstring(s: String, words: Array<String>): List<Int> {
+        val expectedFrequencies = buildTable(words.asSequence())
+        val wordLen = words.first().length
+        val windowSize = wordLen * words.size
+
+        return s
+            .windowed(windowSize)
+            .zip(s.indices)
+            .filter { (window, _) ->
+                val frequencies = buildTable(window, wordLen)
+                frequencies == expectedFrequencies
+            }
+            .map { (_, idx) -> idx }
+            .toList()
+    }
+}

problems/kt/unique-morse-code-words.kt

@@ -0,0 +1,47 @@
+class Solution {
+    val mapping = arrayOf(
+        ".-",
+        "-...",
+        "-.-.",
+        "-..",
+        ".",
+        "..-.",
+        "--.",
+        "....",
+        "..",
+        ".---",
+        "-.-",
+        ".-..",
+        "--",
+        "-.",
+        "---",
+        ".--.",
+        "--.-",
+        ".-.",
+        "...",
+        "-",
+        "..-",
+        "...-",
+        ".--",
+        "-..-",
+        "-.--",
+        "--.."
+    )
+
+    private fun charToMorse(c: Char): String = mapping[c - 'a']
+
+    fun uniqueMorseRepresentations(words: Array<String>): Int =
+        words
+            .map { word ->
+                word.map { charToMorse(it) }.joinToString(separator = "")
+            }
+            .toSet()
+            .size
+}
+
+fun main() {
+    val s = Solution()
+
+    check(s.uniqueMorseRepresentations(arrayOf("gin", "zen", "gig", "msg")) == 2)
+    check(s.uniqueMorseRepresentations(arrayOf("a")) == 1)
+}

problems/kt/validate-binary-search-tree.kt

@@ -0,0 +1,26 @@
+/**
+ * Example:
+ * var ti = TreeNode(5)
+ * var v = ti.`val`
+ * Definition for a binary tree node.
+ * class TreeNode(var `val`: Int) {
+ *     var left: TreeNode? = null
+ *     var right: TreeNode? = null
+ * }
+ */
+class Solution {
+    private data class SpecialRange(val min: Int? = null, val max: Int? = null) {
+        fun check(x: Int): Boolean =
+            (min == null || x > min) && (max == null || x < max)
+    }
+
+    private fun isValidBST(root: TreeNode?, range: SpecialRange): Boolean =
+        when (root) {
+            null -> true
+            else -> range.check(root.`val`)
+                && isValidBST(root.left, range.copy(max=root.`val`))
+                && isValidBST(root.right, range.copy(min=root.`val`))
+        }
+
+    fun isValidBST(root: TreeNode?): Boolean = isValidBST(root, SpecialRange())
+}

problems/kt/word-ladder-ii.kt

@@ -0,0 +1,157 @@
+class Solution {
+    private fun wordDifference(lhs: String, rhs: String): Int = lhs.zip(rhs).count { (l, r) -> l != r }
+
+    private enum class VertexState {
+        Unvisited, Enqueued, Done
+    }
+
+    private data class Vertex<T>(
+        val label: T, val neighbours: MutableSet<Vertex<T>> = mutableSetOf()
+    ) {
+        var distance: Int = Int.MAX_VALUE
+        val parents: MutableSet<Vertex<T>> = mutableSetOf()
+        var state: VertexState = VertexState.Unvisited
+            private set
+
+        fun add(neighbour: Vertex<T>) {
+            neighbours.add(neighbour)
+        }
+
+        fun addParent(parent: Vertex<T>) {
+            parents.add(parent)
+        }
+
+        fun transition() {
+            state = when (state) {
+                VertexState.Unvisited -> VertexState.Enqueued
+                VertexState.Enqueued -> VertexState.Done
+                VertexState.Done -> error("Cannot transition further!")
+            }
+        }
+
+        override fun hashCode(): Int = label.hashCode()
+        override fun toString(): String = "$label(${neighbours.map { it.label.toString() }})"
+        override fun equals(other: Any?): Boolean {
+            if (this === other) return true
+            if (javaClass != other?.javaClass) return false
+
+            other as Vertex<*>
+
+            if (label != other.label) return false
+
+            return true
+        }
+    }
+
+    private class Graph<T> {
+        private val vertices: MutableMap<T, Vertex<T>> = mutableMapOf()
+
+        fun addVertex(src: T, dst: T) {
+            val u = vertices.getOrPut(src) { Vertex(src) }
+            val v = vertices.getOrPut(dst) { Vertex(dst) }
+
+            u.add(v)
+        }
+
+        fun addSymmetricVertex(src: T, dst: T) {
+            addVertex(src, dst)
+            addVertex(dst, src)
+        }
+
+        private fun processVertex(queue: ArrayDeque<Vertex<T>>, u: Vertex<T>) {
+            u.neighbours.forEach { v ->
+                if (v.state == VertexState.Unvisited) {
+                    queue.addLast(v)
+
+                    queue.last().distance = u.distance + 1
+                    queue.last().transition()
+                } else if (u.distance + 1 != v.distance) {
+                    return@forEach
+                }
+
+                v.addParent(u)
+            }
+
+            u.transition()
+        }
+
+        fun bfs(src: T, dst: T) {
+            if (vertices[src] == null) {
+                return
+            }
+
+            val queue = ArrayDeque<Vertex<T>>()
+            queue.addLast(vertices[src]!!)
+
+            queue.last().distance = 0
+            queue.last().transition()
+
+            while (queue.isNotEmpty()) {
+                val u = queue.removeFirst()
+                if (u.label == dst) {
+                    break
+                }
+
+                processVertex(queue, u)
+            }
+        }
+
+        fun parents(vertex: T): List<T> = vertices[vertex]?.parents?.map(Vertex<T>::label) ?: emptyList()
+
+        override fun toString(): String = vertices.toString()
+    }
+
+    private fun constructGraph(src: String, vertices: List<String>): Graph<String> {
+        val g = Graph<String>()
+
+        vertices
+            .filter { wordDifference(src, it) == 1 }
+            .forEach { g.addVertex(src, it) }
+
+        vertices.indices
+            .flatMap { listOf(it).zip(it + 1 until vertices.size) }
+            .map { (i, j) -> vertices[i] to vertices[j] }
+            .filter { (lhs, rhs) -> wordDifference(lhs, rhs) == 1 }
+            .forEach { (lhs, rhs) -> g.addSymmetricVertex(lhs, rhs) }
+
+        return g
+    }
+
+    private fun constructPath(
+        graph: Graph<String>, currentPath: MutableList<String>, paths: MutableList<MutableList<String>>
+    ): MutableList<MutableList<String>> {
+        if (graph.parents(currentPath.last()).isEmpty()) {
+            paths.add(currentPath.reversed().toMutableList())
+            return paths
+        }
+
+        for (parent in graph.parents(currentPath.last()).filter { !currentPath.contains(it) }) {
+            currentPath.add(parent)
+            constructPath(graph, currentPath, paths)
+            currentPath.remove(parent)
+        }
+
+        return paths
+    }
+
+    fun findLadders(
+        beginWord: String, endWord: String, wordList: List<String>
+    ): List<List<String>> {
+        val graph = constructGraph(beginWord, wordList)
+        graph.bfs(beginWord, endWord)
+        return constructPath(graph, mutableListOf(endWord), mutableListOf()).filter { it.count() >= 2 }
+    }
+}
+
+fun main() {
+    val s = Solution()
+
+    check(
+        s.findLadders("hit", "cog", listOf("hot", "dot", "dog", "lot", "log", "cog")) == listOf(
+            listOf("hit", "hot", "dot", "dog", "cog"), listOf("hit", "hot", "lot", "log", "cog")
+        )
+    )
+    check(s.findLadders("hit", "cog", listOf("hot", "dot", "dog", "lot", "log")) == emptyList<List<String>>())
+    check(s.findLadders("hot", "dog", listOf("hot", "dog")) == emptyList<List<String>>())
+    check(s.findLadders("hot", "dog", listOf("hot", "dog", "dot")) == listOf(listOf("hot", "dot", "dog")))
+}