maczyt / exercises Goto Github PK

const memoize = func => {
  const resultMap = new Map();
  return (...args) => {
    let result = resultMap.get(JSON.stringify(args));
    if (result) {
      return result; 
    }
    result = func(...args);
    resultMap.set(JSON.stringify(args), result);
    return result;
  }
}

const binarySearch = (arr, key, start = 0, end = arr.length - 1) => {
  const index = Math.floor((start + end) / 2);
  const middle = arr[index];
  if (middle === key) {
    return index;
  }
  if (index === start || index === end) {
    return -1;
  }
  if (middle < key) {
    return binarySearch(arr, key, index + 1, end);
  } else {
    return binarySearch(arr, key, start, index - 1);
  }
}

const promiseify = func => (...args) => 
  new Promise((resolve, reject) => {
    func(...args, (err, result) => 
         err ? reject(err) : resolve(result)
        )
  })

const parallel = fns => cb => {
  Promise.all(fns.map(fn => promiseify(fn))).then(p => {
    Promise.all(p.map(f => f())).then(result => {
      cb(null, result);
    })
  })
}

const race = fns => cb => {
  Promise.all(fns.map(fn => promiseify(fn))).then(p => {
    Promise.race(p.map(f => f())).then(result => {
      cb(null, result);
    })
  })
}

const　flattenThunk = func => fn => {
  const next = (err, result) => typeof result === 'function' ? result(next) : fn(err, result)
  func(next)
};

const map = (arr, iterator, context) => {
  const mapRes = [];
  for (let i = 0, len = arr.length; i < len; i ++) {
    mapRes.push(iterator.call(context || this, arr[i], i, arr));
  }
  return mapRes;
}