<?php

// get the base frequency
$startingFrequency = 0;

// get the contents given by the advent_of_code website and put it in the folder "external_contents" in the txt file called "day_1.txt"
$fContents = file_get_contents("external_contents/day_1.txt");

$reached = [$startingFrequency];

// Loop through the external contents until we find a match that happens twice
for ($i = 0; $i < 10000; $i++) {
    // loop through each line of the contents (delimit by new line)
    foreach ((array)explode(PHP_EOL, $fContents) as $number) {
        // make sure the number is numeric
        if (is_numeric($number)) {
            // add the number to the starting frequency
            $startingFrequency += $number;
            // check if the starting frequency is in the array
            if (in_array($startingFrequency, $reached)) {
                echo "Duplicate frequency: $startingFrequency<br>";
            } else {
                // push the frequency into the '$reached' array if it has not yet been inserted
                array_push($reached, $startingFrequency);
            }
        }
    }
}


// return the end result
echo "End result: " . $startingFrequency;