Description

InGraphs/PrimMST.js, the method_shiftDown of classPriorityQueue does not give the correct output when a node must be shifted to a left-child leaf without a right-child "brother", which results in a wrong behavior of methodpop.

Expected Behavior

An example of a tree that produces the bug is given by the following array of nodes denoted by their priority:
queue = [0, 1, 2]

ie

1. root node of priority 0
2. left leaf of priority 1
3. right leaf of priority 0

If we call methodpop on this queue, we expect to get the new tree:
queue = [1, 2]

ie

1. root node of priority 1
2. left leaf of priority 2

Actual Behavior

In the case described above, we will get as output a tree represented by:
queue = [2, 1]

ie

1. root node of priority 2
2. left leaf of priority 1

This violates the properties of the heap (we have 2 > 1 but a parent node should never have a bigger value than any of its children).

Steps to reproduce (if applicable)

1. Add an export statement for class PriorityQueue in PrimMST.js

export { PriorityQueue }

2. Add a test filePrimMST.test.js containing the following code

import { PriorityQueue} from '../PrimMST.js'test('Bug in pop method', () => {    // create queue    const queue = new PriorityQueue()    queue.push(0, 0)    queue.push(1, 1)    queue.push(2, 2)    // create expected queue    const expectedQueue = new PriorityQueue()    expectedQueue.push(1, 1)    expectedQueue.push(2, 2)    // result from popping element from the queue    queue.pop()    expect(queue).toEqual(expectedQueue)})

3. Run the tests for PrimMST

npm test -- PrimMST.test.js

Additional information

This is due to the fact that in_shiftDown, the children's priorities are computed under a singletry {} catch {} statement, thus the priority of the left child is set toInfinity if the right child does not exist.