project-euler/custom-methods.js at master · JacobCrofts/project-euler · GitHub

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Number.prototype.isPrime = function() {
  if (this < 2) {
    return false;
  }
  for (var counter = 2; counter <= Math.sqrt(this); counter++) {
    if (this % counter == 0) {
      return false;
    }
  }
  return true;
};

String.prototype.addNumerically = function(otherString) {
  var topNumber = this;
  var bottomNumber = otherString;
  var sum = [];

  if (parseInt(bottomNumber) > parseInt(topNumber)) {
    topNumber = otherString;
    bottomNumber = this;
  }

  while (bottomNumber.length < topNumber.length) {
    bottomNumber = '0' + bottomNumber;
  }

  topNumber.split('').forEach(function(topDigit, index) {
    var bottomDigit = parseInt(bottomNumber[index]) || 0;
    sum.push(parseInt(topDigit) + bottomDigit);
  })

  sum = sum.reverse();

  sum.forEach(function(digit, index) {
    var digits = digit.toString().split('');
    if (digits.length > 1) {
      sum[index] = digits[1];
      var existingDigit = sum[index + 1] || '0'
      sum[index + 1] = parseInt(existingDigit) + parseInt(digits[0]);
    }
  });

  return sum.reverse().join('');
};

String.prototype.multiplyBy = function(otherString) {
  var timesToAdd = parseInt(this);
  var product = "0";
  for (var counter = 0; counter < timesToAdd; counter++) {
    product = product.addNumerically(otherString);
  }
  return product;
};

Number.prototype.primeFactors = function() {
  if (this.isPrime()) {
    return this;
  }
  var possibleFactor = 2
  while (this % possibleFactor != 0) {
    possibleFactor++;
  }
  return [possibleFactor, (this / possibleFactor).primeFactors()].join(',').split(',').map(function(element) {
    return parseInt(element);
  });
};

// too slow to be worth anything with large numbers:

// String.prototype.powerNumerically = function(otherString) {
//   var originalNumber = this;
//   var product = this;
//   for (var counter = 1; counter < parseInt(otherString); counter++) {
//     console.log(product);
//     product = product.multiplyBy(originalNumber);
//   }
//   return product;
// }

// combinations = function(options, length) {
//   if (typeof options[0] != "object") {
//     options = options.map(function(e) {
//       return [e];
//     })
//   }
//   if (length == 1) {
//     return options;
//   }
//   var combos = [];
//   for (var currentIndex = 0; currentIndex < length; currentIndex++) {
//     for (var otherIndex = currentIndex; otherIndex < length; otherIndex++) {
//       // options is an array of arrays...
//       var nextOption = options[currentIndex];
//       nextOption.push(options[otherIndex]);
//       combos.push(nextOption);
//     }
//   }
//   return combinations(combos, length - 1);
// }

// function getCombinations(chars) {
//   var result = [];
//   var f = function(prefix, chars) {
//     for (var i = 0; i < chars.length; i++) {
//       result.push(prefix + chars[i]);
//       f(prefix + chars[i], chars.slice(i + 1));
//     }
//   }
//   f('', chars);
//   return result;
// }

// console.log(getCombinations([1, 22, 3]))