guessTheArray.md

Guess the array

• In this kata, you should guess an unknown number array. You'll be given a function f, which can answer your query in this way:

f a b -- returns an Integral

a and b are indexes of two different elements, and f will return the sum of these two elements.

When a equals b or abs (a - b) is larger than 2, f will raise an error.

Your goal is to find out the correct array.

The whole procedure is like:

• Get the f and the length of the array
• Ask f questions
• Give the correct array according to the answers The array will always be 3 or longer than 3.

Solution:

function guess(f, length) {
  const res = Array(length);
  res[0] = (f(0, 1) + f(0, 2) - f(1, 2)) / 2;
  for (let i = 1; i < length; i++) {
    res[i] = f(i - 1, i) - res[i - 1];
  }
  return res;
}

function f(a, b) {
  const array = [2, 6, 12, 20, 30, 42]; // The unknown array
  return array[a] + array[b];
}

const guessedArray = guess(f, 6);
console.log(guessedArray);