problems: add „126. Word Ladder II“
Signed-off-by: Matej Focko <mfocko@redhat.com>
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157
problems/word-ladder-ii.kt
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157
problems/word-ladder-ii.kt
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class Solution {
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private fun wordDifference(lhs: String, rhs: String): Int = lhs.zip(rhs).count { (l, r) -> l != r }
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private enum class VertexState {
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Unvisited, Enqueued, Done
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}
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private data class Vertex<T>(
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val label: T, val neighbours: MutableSet<Vertex<T>> = mutableSetOf()
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) {
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var distance: Int = Int.MAX_VALUE
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val parents: MutableSet<Vertex<T>> = mutableSetOf()
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var state: VertexState = VertexState.Unvisited
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private set
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fun add(neighbour: Vertex<T>) {
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neighbours.add(neighbour)
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}
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fun addParent(parent: Vertex<T>) {
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parents.add(parent)
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}
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fun transition() {
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state = when (state) {
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VertexState.Unvisited -> VertexState.Enqueued
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VertexState.Enqueued -> VertexState.Done
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VertexState.Done -> error("Cannot transition further!")
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}
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}
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override fun hashCode(): Int = label.hashCode()
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override fun toString(): String = "$label(${neighbours.map { it.label.toString() }})"
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override fun equals(other: Any?): Boolean {
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if (this === other) return true
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if (javaClass != other?.javaClass) return false
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other as Vertex<*>
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if (label != other.label) return false
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return true
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}
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}
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private class Graph<T> {
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private val vertices: MutableMap<T, Vertex<T>> = mutableMapOf()
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fun addVertex(src: T, dst: T) {
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val u = vertices.getOrPut(src) { Vertex(src) }
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val v = vertices.getOrPut(dst) { Vertex(dst) }
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u.add(v)
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}
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fun addSymmetricVertex(src: T, dst: T) {
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addVertex(src, dst)
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addVertex(dst, src)
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}
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private fun processVertex(queue: ArrayDeque<Vertex<T>>, u: Vertex<T>) {
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u.neighbours.forEach { v ->
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if (v.state == VertexState.Unvisited) {
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queue.addLast(v)
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queue.last().distance = u.distance + 1
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queue.last().transition()
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} else if (u.distance + 1 != v.distance) {
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return@forEach
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}
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v.addParent(u)
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}
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u.transition()
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}
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fun bfs(src: T, dst: T) {
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if (vertices[src] == null) {
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return
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}
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val queue = ArrayDeque<Vertex<T>>()
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queue.addLast(vertices[src]!!)
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queue.last().distance = 0
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queue.last().transition()
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while (queue.isNotEmpty()) {
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val u = queue.removeFirst()
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if (u.label == dst) {
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break
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}
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processVertex(queue, u)
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}
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}
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fun parents(vertex: T): List<T> = vertices[vertex]?.parents?.map(Vertex<T>::label) ?: emptyList()
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override fun toString(): String = vertices.toString()
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}
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private fun constructGraph(src: String, vertices: List<String>): Graph<String> {
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val g = Graph<String>()
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vertices
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.filter { wordDifference(src, it) == 1 }
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.forEach { g.addVertex(src, it) }
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vertices.indices
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.flatMap { listOf(it).zip(it + 1 until vertices.size) }
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.map { (i, j) -> vertices[i] to vertices[j] }
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.filter { (lhs, rhs) -> wordDifference(lhs, rhs) == 1 }
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.forEach { (lhs, rhs) -> g.addSymmetricVertex(lhs, rhs) }
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return g
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}
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private fun constructPath(
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graph: Graph<String>, currentPath: MutableList<String>, paths: MutableList<MutableList<String>>
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): MutableList<MutableList<String>> {
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if (graph.parents(currentPath.last()).isEmpty()) {
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paths.add(currentPath.reversed().toMutableList())
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return paths
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}
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for (parent in graph.parents(currentPath.last()).filter { !currentPath.contains(it) }) {
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currentPath.add(parent)
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constructPath(graph, currentPath, paths)
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currentPath.remove(parent)
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}
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return paths
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}
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fun findLadders(
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beginWord: String, endWord: String, wordList: List<String>
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): List<List<String>> {
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val graph = constructGraph(beginWord, wordList)
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graph.bfs(beginWord, endWord)
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return constructPath(graph, mutableListOf(endWord), mutableListOf()).filter { it.count() >= 2 }
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}
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}
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fun main() {
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val s = Solution()
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check(
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s.findLadders("hit", "cog", listOf("hot", "dot", "dog", "lot", "log", "cog")) == listOf(
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listOf("hit", "hot", "dot", "dog", "cog"), listOf("hit", "hot", "lot", "log", "cog")
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)
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)
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check(s.findLadders("hit", "cog", listOf("hot", "dot", "dog", "lot", "log")) == emptyList<List<String>>())
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check(s.findLadders("hot", "dog", listOf("hot", "dog")) == emptyList<List<String>>())
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check(s.findLadders("hot", "dog", listOf("hot", "dog", "dot")) == listOf(listOf("hot", "dot", "dog")))
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}
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