Waiter Discussions |

1 year ago+ 0 comments

I guess that this task is designed to help us prepare for the real challenges of engineering work, as it is a great exercise in dealing with confusing customer requirements ;)

What helped me understand the baffling description and solve the problem was following the proposed analogy with plates, and visualizing how they are being transferred from/to different stacks by the waiter (I even drew a couple of diagrams on a sheet of paper).

JavaScript solution:

function waiter(number, q) {
    // Write your code here
    const answers = [];

    const primes = [];
    let num = 2;
    while (primes.length < q) {
        let isPrime = true;
        for (let div = 2; num > div; div++) {
            if (num % div === 0) {
                isPrime = false;
                break;
            }
        }
        if (isPrime) primes.push(num);
        num++;
    }
    
    function movePlatesOneByOne (fromStack, toStack) {
        for (let i = fromStack.length - 1; i >= 0; i--) {  
            toStack.push(fromStack[i]);
        }
        fromStack.length = 0;
    }

    const plates = number.reverse();
    const stackA = []; // divisible by prime: false
    const stackB = []; // divisible by prime: true

    for (let prime of primes) {
        if (stackA.length) {
            movePlatesOneByOne(stackA, plates);
        }
        
        for (let plate of plates) {
            if (plate % prime === 0) {
                stackB.push(plate);
            } else {
                stackA.push(plate);
            }
        }
        plates.length = 0;
        
        if (stackB.length) {
            movePlatesOneByOne(stackB, answers);
        }
    }
    
    if (stackA.length) {
        movePlatesOneByOne(stackA, answers);
    }
    
    return answers;
}

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