92 lines
3.1 KiB
Swift
92 lines
3.1 KiB
Swift
// Swiftified and further development by (c) 2022 and onwards The vChewing Project (MIT License).
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// Was initially rebranded from (c) Lukhnos Liu's C++ library "Gramambular 2" (MIT License).
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// ====================
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// This code is released under the MIT license (SPDX-License-Identifier: MIT)
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public extension Megrez.Compositor {
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/// 爬軌函式，會更新當前組字器的 walkedNodes。
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///
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/// 找到軌格陣圖內權重最大的路徑。該路徑代表了可被觀測到的最可能的隱藏事件鏈。
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/// 這裡使用 Cormen 在 2001 年出版的教材當中提出的「有向無環圖的最短路徑」的
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/// 算法來計算這種路徑。不過，這裡不是要計算距離最短的路徑，而是計算距離最長
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/// 的路徑（所以要找最大的權重），因為在對數概率下，較大的數值意味著較大的概率。
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/// 對於 `G = (V, E)`，該算法的運行次數為 `O(|V|+|E|)`，其中 `G` 是一個有向無環圖。
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/// 這意味著，即使軌格很大，也可以用很少的算力就可以爬軌。
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/// - Returns: 爬軌結果＋該過程是否順利執行。
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@discardableResult mutating func walk() -> (walkedNode: [Node], succeeded: Bool) {
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var result = [Node]()
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defer { walkedNodes = result }
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guard !spans.isEmpty else { return (result, true) }
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var vertexSpans = [[Vertex]]()
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for _ in spans {
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vertexSpans.append(.init())
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}
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for (i, span) in spans.enumerated() {
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for j in 1 ... span.maxLength {
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if let theNode = span.nodeOf(length: j) {
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vertexSpans[i].append(.init(node: theNode))
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}
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}
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}
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let terminal = Vertex(node: .init(keyArray: ["_TERMINAL_"]))
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var root = Vertex(node: .init(keyArray: ["_ROOT_"]))
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for (i, vertexSpan) in vertexSpans.enumerated() {
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for vertex in vertexSpan {
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let nextVertexPosition = i + vertex.node.spanLength
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if nextVertexPosition == vertexSpans.count {
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vertex.edges.append(terminal)
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continue
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}
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for nextVertex in vertexSpans[nextVertexPosition] {
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vertex.edges.append(nextVertex)
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}
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}
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}
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root.distance = 0
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root.edges.append(contentsOf: vertexSpans[0])
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var ordered = topologicalSort(root: &root)
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for (j, neta) in ordered.reversed().enumerated() {
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for (k, _) in neta.edges.enumerated() {
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relax(u: neta, v: &neta.edges[k])
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}
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ordered[j] = neta
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}
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var iterated = terminal
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var walked = [Node]()
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var totalLengthOfKeys = 0
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while let itPrev = iterated.prev {
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walked.append(itPrev.node)
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iterated = itPrev
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totalLengthOfKeys += iterated.node.spanLength
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}
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// 清理內容，否則會有記憶體洩漏。
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ordered.removeAll()
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vertexSpans.removeAll()
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iterated.destroy()
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root.destroy()
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terminal.destroy()
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guard totalLengthOfKeys == keys.count else {
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print("!!! ERROR A")
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return (result, false)
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}
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guard walked.count >= 2 else {
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print("!!! ERROR B")
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return (result, false)
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}
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walked = walked.reversed()
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walked.removeFirst()
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result = walked
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return (result, true)
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}
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}
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