JOEZACK.COM Code Musings and Such

Project Euler: Problems 1 – 5 in JavaScript

I've been wanting to check out Rhino for a while, and I've been particularly interested in seeing how it compares to Ruby in terms of speed. The results have been a little varied, and it's a deeply flawed comparison. But it's something.

These scripts are just ports of my ruby solutions. There are a few places where I had to roll my own JavaScript functions instead of baked in Ruby methods, but other than that it was nearly line by line translation.

Problem 1 - Ruby solution

Add all the natural numbers below one thousand that are multiples of 3 or 5.

var total = 0;

for(var i = 0; i < 1000; i++) {
  if(i % 3 == 0 || i % 5 == 0) {
    total += i;
  }
}

print(total);

Problem 2 - Ruby solution

Find the sum of all the even-valued terms in the Fibonacci sequence which do not exceed four million.

function fib(stack, n) {
  if(n == 0) {
    return 1;
  }
  if(n == 1) {
    return 2;
  }
  return stack[n - 1] + stack[n - 2];
}

var max   = 4000000;
var total = 0;
var stack = [];

for(var i = 0; i < max; i++) {
  stack[i] = fib(stack,i);
  if(stack[i] > max) {
    break;
  }
  if(stack[i] % 2 == 0) {
    total += stack[i]
  }
}

print(total);

Problem 3 - Ruby solution

Find the largest prime factor of a composite number.

function find_highest_prime_factor(n) {
  var max = Math.round(Math.sqrt(n));
  for(var i = max; i >= 2; i--) {
    if(n % i == 0 && find_highest_prime_factor(i) == 1) {
      return i;
    }
  }
  return 1;
}

var target = 600851475143;
print(find_highest_prime_factor(target));

Problem 4 - Ruby solution

Find the largest palindrome made from the product of two 3-digit numbers.

function get_highest_palindrome(high, low) {
  var highest = 0;
  for(var i = high; i >= low; i--) {
	for(var j = high; j >= low; j--) {
      sum = i * j;
      if(sum <= highest) {
        break;
	  }
      if(is_palindrome(sum.toString())) {
        highest = max(highest, sum);
	  }
    }
  }
  return highest;
}

function reverse(string) {
  var array = string.split('').reverse();
  var out   = '';
  for(key in array) {
	out += array[key];
  }
  return out;
}

function max(a,b) {
  if(a > b) {
	return a;
  }
  return b;
}

function is_palindrome(string) {
  return string == reverse(string);
}

print(get_highest_palindrome(999, 100));

Problem 5 - Ruby solution

What is the smallest number that is evenly divisible by all of the numbers from 1 to 20?

function gcd(a,b) {
  var x = a;
  var y = b;
  var result;

  while (y != 0) {
	result = x % y;
    x      = y;
    y      = result;
  }
  return x;
}

function lcm(a,b) {
  return (a * b) / gcd(a, b);
}

var max = 20;
var min = 11;
var n   = min;

for(var i = min; i <= max; i++) {
  n = lcm(n,i);
}

print(n);