add more test for suffix Tests

Author: michiboo

Sources/Algorithms/Suffix.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift Algorithms open source project
 //
-// Copyright (c) 2020 Apple Inc. and the Swift project authors
+// Copyright (c) 2021 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See https://swift.org/LICENSE.txt for license information
@@ -14,18 +14,17 @@
 //===----------------------------------------------------------------------===//
 
 extension BidirectionalCollection {
-  @inlinable
-  public __consuming func Suffix(while predicate: (Element) throws -> Bool
-  ) rethrows -> [Element] {
-   var result = ContiguousArray<Element>()
-   self.reverse()
-    for element in self {
-      guard try predicate(element) else {
-        break
-      }
-      result.append(element)
+  public func suffix(
+    while predicate: (Element) throws -> Bool
+  ) rethrows -> SubSequence {
+    let start = startIndex
+    var result = endIndex
+    while result != start {
+      let previous = index(before: result)
+      guard try predicate(self[previous]) else { break }
+
+      result = previous
     }
-    result.reverse()
-    return Array(result)
+    return self[result...]
   }
-}
+}

Tests/SwiftAlgorithmsTests/SuffixTests.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift Algorithms open source project
 //
-// Copyright (c) 2020 Apple Inc. and the Swift project authors
+// Copyright (c) 2021 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See https://swift.org/LICENSE.txt for license information
@@ -17,4 +17,9 @@ final class SuffixTests: XCTestCase {
   func testSuffix() {
     let a = 0...10
     XCTAssertEqualSequences(a.suffix(while: { $0 > 5 }), (6...10))
+    XCTAssertEqualSequences(a.suffix(while: { $0 > 10 }), [])
+    XCTAssertEqualSequences(a.suffix(while: { $0 > 9 }), [9])
+    XCTAssertEqualSequences(a.suffix(while: { $0 > -1 }), (0...10))
+    let empty = (0...).prefix(0)
+    XCTAssertEqualSequences(empty.suffix(while: { $0 > 10 }), [])
 }