fixes: #774 - add test and fix MinPriorityQueue implementation

Data-Structures/Heap/MinPriorityQueue.js

@@ -57,13 +57,22 @@ class MinPriorityQueue {
     output(this.heap.slice(1))
   }
 
-  // heap sorting can be done by performing
-  // delete function to the number of times of the size of the heap
-  // it returns reverse sort because it is a min priority queue
-  heapSort () {
-    for (let i = 1; i < this.capacity; i++) {
-      this.delete()
+  // heap reverse can be done by performing swaping the first
+  // element with the last, removing the last element to
+  // new array and calling sink function.
+  heapReverse () {
+    const heapSort = []
+    while (this.size > 0) {
+      // swap first element with last element
+      [this.heap[1], this.heap[this.size]] = [this.heap[this.size], this.heap[1]]
+      heapSort.push(this.heap.pop())
+      this.size--
+      this.sink()
     }
+    // first value from heap it's empty to respect
+    // structure with 1 as index of the first element
+    this.heap = [undefined, ...heapSort.reverse()]
+    this.size = heapSort.length
   }
 
   // this function reorders the heap after every delete function
@@ -98,11 +107,17 @@ class MinPriorityQueue {
     }
   }
 
-  // deletes the highest priority value from the heap
+  // deletes the highest priority value from the heap. The last
+  // element goes to ahead to first position and reorder heap
   delete () {
+    // checks empty and one element array conditions
+    if (this.isEmpty()) return
+    if (this.size === 1) {
+      this.size--
+      return this.heap.pop()
+    }
     const min = this.heap[1]
-    this.heap[1] = this.heap[this.size]
-    this.heap[this.size] = min
+    this.heap[1] = this.heap.pop()
     this.size--
     this.sink()
     return min

Data-Structures/Heap/test/MinPriorityQueue.test.js

@@ -3,14 +3,16 @@ import { MinPriorityQueue } from '../MinPriorityQueue'
 describe('MinPriorityQueue', () => {
   const values = [5, 2, 4, 1, 7, 6, 3, 8]
   const capacity = values.length
+  let queue
 
-  const Queue = new MinPriorityQueue(capacity)
-
-  values.forEach(v => Queue.insert(v))
+  beforeEach(() => {
+    queue = new MinPriorityQueue(capacity)
+    values.forEach(v => queue.insert(v))
+  })
 
   it('Check heap ordering', () => {
     const mockFn = jest.fn()
-    Queue.print(mockFn)
+    queue.print(mockFn)
 
     expect(mockFn.mock.calls.length).toBe(1) // Expect one call
     expect(mockFn.mock.calls[0].length).toBe(1) // Expect one argument
@@ -21,10 +23,9 @@ describe('MinPriorityQueue', () => {
   })
 
   it('heapSort() expected to reverse the heap ordering', () => {
-    Queue.heapSort()
-
+    queue.heapReverse()
     const mockFn = jest.fn()
-    Queue.print(mockFn)
+    queue.print(mockFn)
 
     expect(mockFn.mock.calls.length).toBe(1)
     expect(mockFn.mock.calls[0].length).toBe(1)
@@ -33,4 +34,22 @@ describe('MinPriorityQueue', () => {
     expect(heap.length).toBe(capacity)
     expect(heap).toStrictEqual([8, 7, 6, 5, 4, 3, 2, 1])
   })
+
+  describe('delete() function work properly', () => {
+    it('return undefined if heap is empty', () => {
+      const minqueue = new MinPriorityQueue(capacity)
+      const min = minqueue.delete()
+      expect(min).toBe(undefined)
+    })
+    it('return min value and remove it', () => {
+      const sortedValues = values.sort()
+      let initialSize = queue.size
+      sortedValues.forEach((minValue, index) => {
+        const min = queue.delete()
+        expect(min).toBe(minValue)
+        expect(queue.size).toBe(--initialSize)
+      })
+      expect(queue.size).toBe(0)
+    })
+  })
 })