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oleole
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Merge pull request #21 from kareman/binary-search-recursion
Simplify binary search using recursion.
2 parents 68c2606 + f53d5f0 commit b1c8105

3 files changed

Lines changed: 172 additions & 19 deletions

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‎SortedArray.xcodeproj/xcshareddata/xcschemes/Performance test-macOS.xcscheme‎

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<?xml version="1.0" encoding="UTF-8"?>
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<Scheme
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LastUpgradeVersion = "0900"
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version = "1.3">
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<BuildAction
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parallelizeBuildables = "YES"
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buildImplicitDependencies = "YES">
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<BuildActionEntries>
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<BuildActionEntry
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buildForTesting = "YES"
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buildForRunning = "YES"
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buildForProfiling = "YES"
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buildForArchiving = "YES"
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buildForAnalyzing = "YES">
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<BuildableReference
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BuildableIdentifier = "primary"
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BlueprintIdentifier = "52D6DA0E1BF000BD002C0205"
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BuildableName = "SortedArray.framework"
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BlueprintName = "SortedArray-macOS"
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ReferencedContainer = "container:SortedArray.xcodeproj">
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buildConfiguration = "Release"
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selectedDebuggerIdentifier = ""
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selectedLauncherIdentifier = "Xcode.IDEFoundation.Launcher.PosixSpawn"
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disableMainThreadChecker = "YES"
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language = ""
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shouldUseLaunchSchemeArgsEnv = "YES">
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skipped = "NO">
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BuildableIdentifier = "primary"
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BlueprintIdentifier = "DD7502791C68FCFC006590AF"
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BuildableName = "SortedArray-macOS Tests.xctest"
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BlueprintName = "SortedArray-macOS Tests"
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ReferencedContainer = "container:SortedArray.xcodeproj">
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</BuildableReference>
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<SkippedTests>
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<Test
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Identifier = "SortedArrayTests">
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</Test>
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</SkippedTests>
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</TestableReference>
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</Testables>
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BuildableIdentifier = "primary"
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BuildableName = "SortedArray.framework"
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BlueprintName = "SortedArray-macOS"
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ReferencedContainer = "container:SortedArray.xcodeproj">
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buildConfiguration = "Release"
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selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
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selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
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language = ""
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useCustomWorkingDirectory = "NO"
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debugDocumentVersioning = "YES"
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debugServiceExtension = "internal"
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allowLocationSimulation = "YES">
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</Scheme>

‎Sources/SortedArray.swift‎

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@@ -358,6 +358,13 @@ fileprivate enum Match<Index: Comparable> {
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case notFound(insertAt: Index)
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}
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extension Range where Bound == Int {
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var middle: Int? {
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guard !isEmpty else { return nil }
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return lowerBound + count / 2
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}
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}
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extension SortedArray {
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/// Searches the array for `element` using binary search.
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///
@@ -375,26 +382,15 @@ extension SortedArray {
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}
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fileprivate func search(for element: Element, in range: Range<Index>) -> Match<Index> {
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guard !range.isEmpty else { return .notFound(insertAt: range.upperBound) }
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var left = range.lowerBound
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var right = index(before: range.upperBound)
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while left <= right {
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let dist = distance(from: left, to: right)
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let mid = index(left, offsetBy: dist/2)
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let candidate = self[mid]
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switch compare(candidate, element) {
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case .orderedAscending:
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left = index(after: mid)
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case .orderedDescending:
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right = index(before: mid)
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case .orderedSame:
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return .found(at: mid)
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}
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guard let middle = range.middle else { return .notFound(insertAt: range.upperBound) }
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switch compare(element, self[middle]) {
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case .orderedDescending:
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return search(for: element, in: index(after: middle)..<range.upperBound)
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case .orderedAscending:
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return search(for: element, in: range.lowerBound..<middle)
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case .orderedSame:
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return .found(at: middle)
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}
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// Not found. left is the index where this element should be placed if it were inserted.
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return .notFound(insertAt: left)
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}
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}
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‎Tests/SortedArrayTests/PerformanceTests.swift‎

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@@ -29,6 +29,52 @@ class PerformanceTests: XCTestCase {
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XCTAssertEqual(sut.lastIndex(of: 3), 999_999)
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}
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}
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func testPerformanceOfIndexOfObject() {
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let sourceArray = Array(repeating: Box(500), count: 1_000_000) + Array(repeating: Box(40), count: 1_000_000) + Array(repeating: Box(3), count: 1_000_000)
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let sut = SortedArray(unsorted: sourceArray)
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measure {
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XCTAssertEqual(sut.index(of: Box(500)), 2_000_000)
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}
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}
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func testPerformanceOfLastIndexOfObject() {
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let sourceArray = Array(repeating: Box(500), count: 1_000_000) + Array(repeating: Box(40), count: 1_000_000) + Array(repeating: Box(3), count: 1_000_000)
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let sut = SortedArray(unsorted: sourceArray)
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measure {
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XCTAssertEqual(sut.lastIndex(of: Box(3)), 999_999)
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}
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}
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func testPerformanceOfIndexOfObjectInRange() {
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let sut = SortedArray(sorted: (0..<3_000_000).lazy.map(Box.init))
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measure {
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XCTAssertEqual(sut.index(of: Box(500)), 500)
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}
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}
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func testPerformanceOfLastIndexOfObjectInRange() {
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let sut = SortedArray(sorted: (0..<3_000_000).lazy.map(Box.init))
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XCTAssertEqual(sut.lastIndex(of: Box(1_999_999)), 1_999_999)
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measure {
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XCTAssertEqual(sut.lastIndex(of: Box(1_999_999)), 1_999_999)
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}
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}
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}
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class Box<T: Comparable>: Comparable {
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static func <(lhs: Box<T>, rhs: Box<T>) -> Bool {
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return lhs.value < rhs.value
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}
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static func ==(lhs: Box<T>, rhs: Box<T>) -> Bool {
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return lhs.value == rhs.value
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}
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let value: T
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init(_ value: T) {
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self.value = value
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}
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}
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extension PerformanceTests {
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("testLinuxTestSuiteIncludesAllTests", testLinuxTestSuiteIncludesAllTests),
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("testPerformanceOfIndexOf", testPerformanceOfIndexOf),
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("testPerformanceOfLastIndexOf", testPerformanceOfLastIndexOf),
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("testPerformanceOfIndexOfObject", testPerformanceOfIndexOfObject),
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("testPerformanceOfLastIndexOfObject", testPerformanceOfLastIndexOfObject),
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("testPerformanceOfIndexOfObjectInRange", testPerformanceOfIndexOfObjectInRange),
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("testPerformanceOfLastIndexOfObjectInRange", testPerformanceOfLastIndexOfObjectInRange),
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]
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}
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}

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