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| 1 | +package org.jetbrains.kotlinx.dataframe.impl |
| 2 | + |
| 3 | +import kotlin.experimental.ExperimentalTypeInference |
| 4 | + |
| 5 | +/** |
| 6 | + * Represents a directed acyclic graph (DAG) of generic type [T]. |
| 7 | + * |
| 8 | + * This class is immutable and guarantees that the graph does not contain any cycles. |
| 9 | + * It provides functionality to find the nearest common ancestor of two vertices |
| 10 | + * in the graph ([findNearestCommonVertex]). |
| 11 | + * |
| 12 | + * Use the [Builder] class or [buildDag] function to create a new instance of this class. |
| 13 | + * |
| 14 | + * @param T The type of items in the graph. |
| 15 | + * @property adjacencyList A map representing directed edges, where the keys are source vertices |
| 16 | + * and the values are sets of destination vertices. |
| 17 | + * @property vertices A set of all vertices in the graph. |
| 18 | + */ |
| 19 | +internal class DirectedAcyclicGraph<T> private constructor( |
| 20 | + private val adjacencyList: Map<T, Set<T>>, |
| 21 | + private val vertices: Set<T>, |
| 22 | +) { |
| 23 | + class Builder<T> { |
| 24 | + private val edges = mutableListOf<Pair<T, T>>() |
| 25 | + private val vertices = mutableSetOf<T>() |
| 26 | + |
| 27 | + fun addEdge(from: T, to: T): Builder<T> { |
| 28 | + edges.add(from to to) |
| 29 | + vertices.add(from) |
| 30 | + vertices.add(to) |
| 31 | + return this |
| 32 | + } |
| 33 | + |
| 34 | + fun addEdges(vararg edges: Pair<T, T>): Builder<T> { |
| 35 | + edges.forEach { (from, to) -> addEdge(from, to) } |
| 36 | + return this |
| 37 | + } |
| 38 | + |
| 39 | + fun build(): DirectedAcyclicGraph<T> { |
| 40 | + val adjacencyList = edges.groupBy({ it.first }, { it.second }) |
| 41 | + .mapValues { it.value.toSet() } |
| 42 | + |
| 43 | + if (hasCycle(adjacencyList)) { |
| 44 | + throw IllegalStateException("Graph contains cycle") |
| 45 | + } |
| 46 | + |
| 47 | + return DirectedAcyclicGraph(adjacencyList, vertices) |
| 48 | + } |
| 49 | + |
| 50 | + private fun hasCycle(adjacencyList: Map<T, Set<T>>): Boolean { |
| 51 | + val visited = mutableSetOf<T>() |
| 52 | + val recursionStack = mutableSetOf<T>() |
| 53 | + |
| 54 | + fun dfs(vertex: T): Boolean { |
| 55 | + if (vertex in recursionStack) return true |
| 56 | + if (vertex in visited) return false |
| 57 | + |
| 58 | + visited.add(vertex) |
| 59 | + recursionStack.add(vertex) |
| 60 | + |
| 61 | + adjacencyList[vertex]?.forEach { neighbor -> |
| 62 | + if (dfs(neighbor)) return true |
| 63 | + } |
| 64 | + |
| 65 | + recursionStack.remove(vertex) |
| 66 | + return false |
| 67 | + } |
| 68 | + |
| 69 | + return adjacencyList.keys.any { vertex -> |
| 70 | + if (vertex !in visited && dfs(vertex)) return true |
| 71 | + false |
| 72 | + } |
| 73 | + } |
| 74 | + } |
| 75 | + |
| 76 | + fun findNearestCommonVertex(vertex1: T, vertex2: T): T? { |
| 77 | + if (vertex1 !in vertices || vertex2 !in vertices) return null |
| 78 | + if (vertex1 == vertex2) return vertex1 |
| 79 | + |
| 80 | + // Get all ancestors for both vertices |
| 81 | + val ancestors1 = getAllAncestors(vertex1) |
| 82 | + val ancestors2 = getAllAncestors(vertex2) |
| 83 | + |
| 84 | + // If one vertex is an ancestor of another, return that vertex |
| 85 | + if (vertex1 in ancestors2) return vertex1 |
| 86 | + if (vertex2 in ancestors1) return vertex2 |
| 87 | + |
| 88 | + // Find common ancestors |
| 89 | + val commonAncestors = ancestors1.intersect(ancestors2) |
| 90 | + if (commonAncestors.isEmpty()) return null |
| 91 | + |
| 92 | + // Find the nearest common ancestor by checking distance from both vertices |
| 93 | + return commonAncestors.minByOrNull { ancestor -> |
| 94 | + getDistance(ancestor, vertex1) + getDistance(ancestor, vertex2) |
| 95 | + } |
| 96 | + } |
| 97 | + |
| 98 | + private fun getAllAncestors(vertex: T): Set<T> { |
| 99 | + val ancestors = mutableSetOf<T>() |
| 100 | + val visited = mutableSetOf<T>() |
| 101 | + |
| 102 | + fun dfs(current: T) { |
| 103 | + if (current in visited) return |
| 104 | + visited.add(current) |
| 105 | + |
| 106 | + adjacencyList.forEach { (parent, children) -> |
| 107 | + if (current in children) { |
| 108 | + ancestors.add(parent) |
| 109 | + dfs(parent) |
| 110 | + } |
| 111 | + } |
| 112 | + } |
| 113 | + |
| 114 | + dfs(vertex) |
| 115 | + return ancestors |
| 116 | + } |
| 117 | + |
| 118 | + private fun getDistance(from: T, to: T): Int { |
| 119 | + if (from == to) return 0 |
| 120 | + |
| 121 | + val distances = mutableMapOf<T, Int>() |
| 122 | + val queue = ArrayDeque<T>() |
| 123 | + |
| 124 | + queue.add(from) |
| 125 | + distances[from] = 0 |
| 126 | + |
| 127 | + while (queue.isNotEmpty()) { |
| 128 | + val current = queue.removeFirst() |
| 129 | + val currentDistance = distances[current] ?: continue |
| 130 | + |
| 131 | + adjacencyList[current]?.forEach { neighbor -> |
| 132 | + if (neighbor !in distances) { |
| 133 | + distances[neighbor] = currentDistance + 1 |
| 134 | + queue.add(neighbor) |
| 135 | + if (neighbor == to) return currentDistance + 1 |
| 136 | + } |
| 137 | + } |
| 138 | + } |
| 139 | + |
| 140 | + return Int.MAX_VALUE |
| 141 | + } |
| 142 | + |
| 143 | + fun <R> map(conversion: (T) -> R): DirectedAcyclicGraph<R> { |
| 144 | + val cache = mutableMapOf<T, R>() |
| 145 | + val cachedConversion: (T) -> R = { cache.getOrPut(it) { conversion(it) } } |
| 146 | + |
| 147 | + return Builder<R>().apply { |
| 148 | + for ((from, to) in adjacencyList) { |
| 149 | + for (to in to) { |
| 150 | + addEdge(from = cachedConversion(from), to = cachedConversion(to)) |
| 151 | + } |
| 152 | + } |
| 153 | + }.build() |
| 154 | + } |
| 155 | + |
| 156 | + companion object { |
| 157 | + fun <T> builder(): Builder<T> = Builder() |
| 158 | + } |
| 159 | +} |
| 160 | + |
| 161 | +/** |
| 162 | + * Builds a new [DirectedAcyclicGraph] using the provided [builder] function. |
| 163 | + * |
| 164 | + * @see DirectedAcyclicGraph |
| 165 | + */ |
| 166 | +@OptIn(ExperimentalTypeInference::class) |
| 167 | +internal fun <T> buildDag( |
| 168 | + @BuilderInference builder: DirectedAcyclicGraph.Builder<T>.() -> Unit, |
| 169 | +): DirectedAcyclicGraph<T> = DirectedAcyclicGraph.builder<T>().apply(builder).build() |
| 170 | + |
| 171 | +/** |
| 172 | + * Builds a new [DirectedAcyclicGraph] using the provided [edges]. |
| 173 | + * |
| 174 | + * @see DirectedAcyclicGraph |
| 175 | + */ |
| 176 | +internal fun <T> dagOf(vararg edges: Pair<T, T>): DirectedAcyclicGraph<T> = buildDag { addEdges(*edges) } |
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