<?php

	$list1 = ['a','b','c'];
	$list2 = [1,2,3];

	$list3 = mix($list1, $list2);
	print_r($list3);

	function mix($list1, $list2) {

		if(!is_array($list1) || !is_array($list2))
			return "Invalid input values!";

		if(empty($list1) && empty($list2))
			return "The arrays are empty!";

		$i=0;
		foreach($list1 as $l1) {
			array_splice($list2, $i, 0, array($l1));
			$i+=2;
		}

		return $list2;
	}