Project Euler #15

Posted on October 7th, 2012

This is just a short little post about some fun I had this afternoon. Hopefully soon I’ll be starting a game app using canvas and jquery and will have much more useful and exciting things to say.

Project Euler Problem number fifteen is as follows:

Starting in the top left corner of a 2X2 grid, there are 6 routes (without backtracking) to the bottom right corner. How many routes are there through a 20X20 grid?

I decided to take a mathematical approach to it since my math is pretty crusty and that depresses me. So, I got pretty quickly caught up on my combinations/Binomial Coefficient and wrote a little Python and here it is:

import math

# Below assumes a square
def getit(a):
    test = math.factorial(a*2)/math.factorial(a)**2
    print test


I made one that doesn’t depend on equal number sides as well, but am not sure if it’s correct yet. It is (along with this) in github.

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ProjectEuler Problems 18/67 Solution. At Last!

Posted on September 3rd, 2012

I’ve been using as a fun way to practice solving logic problems. For whatever reason, I got stuck on #18 (which is the same as #67, the difference being 67 cannot be solved using brute force) and skipped over it. Just could not figure out how not to add every possible path! Yesterday I finally came up with a solution, tested it out today and it’s super fast.

Here you go, in PHP:

NOTE: The syntax highlighter is really messing up my code, but it can be viewed here in github.

$handle = @fopen("input.txt", "r");
$tri_array = array();
while (($buffer = fgets($handle)) !== false){
    $tri_array[] = explode(" ", $buffer);
$x = count($tri_array)- 1;
$new_row = $tri_array[$x];
while($x > 0){
    $row = $tri_array[$x];
    $temp_arr = array();
    foreach($row as $key=>$value){
            $temp_arr[] = $new_row[$key] > $new_row[$key + 1] ? $value + $new_row[$key] : $value + $new_row[$key + 1];
    $new_row = $temp_arr;

Super easy!

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