quiz.js

'use strict';

// Quiz:
//
// Implement `solution` function using only calls to API methods below and no
// other JS primitives (even math).
//
// Correct implementation will print "Success!" once executed
//

function solution(initial) {
  return initial;
}

check(solution([ [ +1, 1, 2, 3, 4 ], [ -1, 3, 4, 1, 2 ] ]));

//
// API
//

// Example:
//
// join([ [ +1, 1, 2, 3, 4] , [ +1, 4, 3, 2, 1 ] ],
//      [ [ -1, 1, 2, 3, 4] ])
//
// Result:
//
// [ [ +1, 4, 3, 2, 1 ] ]
//
function join(a, b) {
  const res = a.concat(b);

  res.sort((a, b) => {
    for (let i = 1; i <= 4; i++)
      if (a[i] < b[i])
        return -1;
      else if (a[i] > b[i])
        return 1;
    return a[0] - b[0];
  });

  return res.reduce((acc, curr) => {
    if (acc.length === 0)
      return [ curr ];

    const last = acc[acc.length - 1];
    const same = last.slice(1).every((val, i) => {
      return val === curr[i + 1];
    });

    if (!same)
      return acc.concat([ curr ]);

    last[0] += curr[0];
    return acc;
  }, []).filter(item => item[0] !== 0);
}

// Replace +1234 at `at` with:
// -1342 -1423
function b(arr, at) {
  const res = [];
  arr.forEach((item, i) => {
    if (at !== undefined && i !== at)
      return res.push(item);

    res.push(
      [ -item[0], item[1], item[3], item[4], item[2] ],
      [ -item[0], item[1], item[4], item[2], item[3] ]
    );
  });
  return join([], res);
}

// Replace +1234 at `at` with:
// -2134
function s1(arr, at) {
  return join([], arr.map((item, i) => {
    if (at !== undefined && i !== at)
      return item;

    return [ -item[0], item[2], item[1], item[3], item[4] ];
  }));
}

// Replace +1234 at `at` with:
// -1243
function s2(arr, at) {
  return join([], arr.map((item, i) => {
    if (at !== undefined && i !== at)
      return item;

    return [ -item[0], item[1], item[2], item[4], item[3] ];
  }));
}

// Swap `i` with `j` in all numbers
function swap(arr, i, j) {
  return arr.map((item) => {
    return [ item[0] ].concat(item.slice(1).map((value) => {
      if (value === i)
        return j;
      else if (value === j)
        return i;
      else
        return value;
    }));
  });
}

function inspect(arr) {
  console.log(arr.map((item) => {
    const multiplier = item[0];

    const prefix = multiplier === 1 ? '+' :
                   multiplier === -1 ? '-' :
                   multiplier.toString() + ' * ';

    return prefix + item.slice(1).join('');
  }).join(' '));
}

function check(arr) {
  if (arr.length === 0)
    return console.log('Success!');

  inspect(arr);
  throw new Error('Solution incomplete, must return empty array');
}