Collatz Solve

collatz.php

<?php
/*
The following iterative sequence is defined for the set of positive integers:

n → n / 2 (n is even)
n → 3n + 1 (n is odd)

Using the rule above and starting with 13, we generate the following sequence:

13 → 40 → 20 → 10 → 5 → 16 → 8 → 4 → 2 → 1

It can be seen that this sequence (starting at 13 and finishing at 1) contains 10 terms. Although it has not been proved yet (Collatz Problem), it is thought that all starting numbers finish at 1 (and for this interview you may assume this is correct).
Which starting number, under one million, produces the longest chain?
*/
// TIMH Solution VV

function collatz_calc($starting_num,$all_vals) {
	$chain_len = 0;
	$current_val = $starting_num;

	while($current_val != 1) {
		// Do we already know the rest?
		if(isset($all_vals[$current_val])) {
			return $chain_len + $all_vals[$current_val];
		}
		if(($current_val % 2) == 0) {
			// even case
			$current_val = (int)($current_val / 2);
			$chain_len++;
		} else {
			// Odd case
			$current_val = (int)($current_val * 3 + 1);
			$chain_len++;
		}
	}

	$chain_len++;

	return $chain_len;
}


$max_val = ['val'=>1,'chain_len'=>1];

$all_vals = [];

for ( $i = 2; $i < 1000000; $i++) {
	$current_len = collatz_calc($i,$all_vals);
	$all_vals[$i] = $current_len;
	//echo "Val: $i Chain Length: $current_len\n";
	if($current_len > $max_val['chain_len']) {
		$max_val['val'] = $i;
		$max_val['chain_len'] = $current_len;
	}
}


print_r($max_val);