Processing index out of bounds

Author: lixianwa

Heap/Heap.swift

@@ -112,6 +112,8 @@ public struct Heap<T> {
    * larger than the old one; in a min-heap it should be smaller.
    */
   public mutating func replace(index i: Int, value: T) {
+    guard i < elements.count else { return }
+    
     assert(isOrderedBefore(value, elements[i]))
     elements[i] = value
     shiftUp(index: i)
@@ -141,6 +143,8 @@ public struct Heap<T> {
    * to know the node's index, which may actually take O(n) steps to find.
    */
   public mutating func removeAtIndex(i: Int) -> T? {
+    guard i < elements.count else { return nil }
+    
     let size = elements.count - 1
     if i != size {
       swap(&elements[i], &elements[size])

Heap/Tests/HeapTests.swift

@@ -196,6 +196,12 @@ class HeapTests: XCTestCase {
     XCTAssertTrue(verifyMaxHeap(h))
     XCTAssertEqual(h.elements, [100, 50, 70, 10, 20, 60, 65])
 
+    //test index out of bounds
+    let v = h.removeAtIndex(10)
+    XCTAssertEqual(v, nil)
+    XCTAssertTrue(verifyMaxHeap(h))
+    XCTAssertEqual(h.elements, [100, 50, 70, 10, 20, 60, 65])
+    
     let v1 = h.removeAtIndex(5)
     XCTAssertEqual(v1, 60)
     XCTAssertTrue(verifyMaxHeap(h))
@@ -308,5 +314,10 @@ class HeapTests: XCTestCase {
     h.replace(index: 5, value: 13)
     XCTAssertTrue(verifyMaxHeap(h))
     XCTAssertEqual(h.elements, [16, 14, 13, 8, 7, 10, 3, 2, 4, 1])
+    
+    //test index out of bounds
+    h.replace(index: 20, value: 2)
+    XCTAssertTrue(verifyMaxHeap(h))
+    XCTAssertEqual(h.elements, [16, 14, 13, 8, 7, 10, 3, 2, 4, 1])
   }
 }