Fix heapify stopping before it should

Author: rockbruno

Sources/Algorithms/PartialSort.swift

@@ -174,7 +174,7 @@ extension MutableCollection where Self: RandomAccessCollection {
       return
     }
     var heapEndIndex = 0
-    for i in ((count / 2) + 1)..<count {
+    for i in (count / 2)..<count {
       try siftDown(i, by: areInIncreasingOrder, heapEndIndex: heapEndIndex)
     }
     var iterator = (0..<k).makeIterator()

Tests/SwiftAlgorithmsTests/PartialSortTests.swift

@@ -15,48 +15,74 @@ import Algorithms
 final class PartialSortTests: XCTestCase {
   func testEmpty() {
     let array = [Int]()
-
     XCTAssertEqual(array.partiallySorted(0), [])
   }
 
-  func testPartialSortComparable() {
+  func testPartialSortWithPriority() {
     let array: [Int] = [20, 1, 4, 70, 100, 2, 3, 7, 90]
 
-    XCTAssertEqual(array.partiallySorted(0), array)
+    XCTAssertEqual(array.partiallySorted(0, by: >), array)
+    XCTAssertEqual(
+      array.partiallySorted(1, by: >),
+      [100, 1, 4, 3, 7, 20, 70, 90, 2]
+    )
 
     XCTAssertEqual(
-      array.partiallySorted(1),
-      [1, 90, 4, 70, 100, 7, 3, 2, 20]
+      array.partiallySorted(5, by: >),
+      [100, 90, 70, 20, 7, 2, 4, 3, 1]
     )
 
     XCTAssertEqual(
-      array.partiallySorted(5),
+      array.partiallySorted(9, by: >),
+      [100, 90, 70, 20, 7, 4, 3, 2, 1]
+    )
+
+    XCTAssertEqual([0, 1].partiallySorted(1, by: <), [0, 1])
+    XCTAssertEqual([1, 0].partiallySorted(1, by: <), [0, 1])
+    XCTAssertEqual([1, 0].partiallySorted(2, by: <), [0, 1])
+    XCTAssertEqual([0, 1].partiallySorted(1, by: >), [1, 0])
+    XCTAssertEqual([1, 0].partiallySorted(1, by: >), [1, 0])
+    XCTAssertEqual([1, 0].partiallySorted(2, by: >), [1, 0])
+    
+    XCTAssertEqual(
+      [1, 2, 3, 4, 7, 20, 70, 90, 100].partiallySorted(5, by: <),
       [1, 2, 3, 4, 7, 90, 70, 20, 100]
     )
 
     XCTAssertEqual(
-      array.partiallySorted(9),
-      [1, 2, 3, 4, 7, 20, 70, 90, 100]
+      [1, 2, 3, 4, 7, 20, 70, 90, 100].partiallySorted(5, by: >),
+      [100, 90, 70, 20, 7, 2, 4, 3, 1]
+    )
+
+    XCTAssertEqual(
+      [1, 2, 3, 4, 7, 20, 70, 90, 100].partiallySorted(5, by: >),
+      [100, 90, 70, 20, 7, 2, 4, 3, 1]
+    )
+
+    XCTAssertEqual(
+      [1, 2, 3, 4, 7, 20, 70, 90, 100].partiallySorted(5, by: <),
+      [1, 2, 3, 4, 7, 90, 70, 20, 100]
     )
   }
 
-  func testPartialSortComparableWithCustomPriority() {
+  func testPartialSortComparable() {
     let array: [Int] = [20, 1, 4, 70, 100, 2, 3, 7, 90]
 
-    XCTAssertEqual(array.partiallySorted(0, by: >), array)
+    XCTAssertEqual(array.partiallySorted(0), array)
+
     XCTAssertEqual(
-      array.partiallySorted(1, by: >),
-      [100, 1, 4, 3, 7, 20, 70, 90, 2]
+      array.partiallySorted(1),
+      [1, 90, 4, 70, 100, 7, 3, 2, 20]
     )
 
     XCTAssertEqual(
-      array.partiallySorted(5, by: >),
-      [100, 90, 70, 20, 7, 2, 4, 3, 1]
+      array.partiallySorted(5),
+      [1, 2, 3, 4, 7, 90, 70, 20, 100]
     )
 
     XCTAssertEqual(
-      array.partiallySorted(9, by: >),
-      [100, 90, 70, 20, 7, 4, 3, 2, 1]
+      array.partiallySorted(9),
+      [1, 2, 3, 4, 7, 20, 70, 90, 100]
     )
   }
 
@@ -91,16 +117,4 @@ final class PartialSortTests: XCTestCase {
       [1, 2, 3, 4, 7, 20, 70, 90, 100]
     )
   }
-
-  func testPartialSortDescendingArray() {
-    let array: [Int] = [100, 90, 70, 20, 7, 4, 3, 2, 1]
-
-    XCTAssertEqual(array.partiallySorted(9, by: >), array)
-  }
-
-  func testPartialSortAscendingArray() {
-    let array: [Int] = [1, 2, 3, 4, 7, 20, 70, 90, 100]
-
-    XCTAssertEqual(array.partiallySorted(9, by: <), array)
-  }
 }