Part 1
Code Code Code ……
<?php
$head = 0;
$arr = array("a", "b", "c", "d", "e", "f", "g", "h");
function convertIndex($index){
global $arr, $head;
$newIndex = $index+$head;
while($newIndex < 0){
$newIndex += sizeof($arr);
}
return $newIndex%sizeof($arr);
}
function getCharAt($index)
{
global $arr, $head;
$newIndex =convertIndex($index);
return $arr[$newIndex];
}
function setCharAt($index, $value)
{
global $arr, $head;
$arr[convertIndex($index)] = $value;
}
function swapPos($pos1, $pos2) {
$tmp1 = getCharAt($pos1);
$tmp2 = getCharAt($pos2);
setCharAt($pos1, $tmp2);
setCharAt($pos2, $tmp1);
}
function swapLetters($letter1, $letter2) {
global $arr;
$index1 = array_search($letter1, $arr);
$index2 = array_search($letter2, $arr);
$arr[$index2] = $letter1;
$arr[$index1] = $letter2;
}
function reverse($pos1, $pos2) {
for ($i = $pos1, $j=$pos2; $i < $j; $i++, $j--){
swapPos($i, $j);
}
}
function printArray() {
global $arr;
for ($i = 0; $i < sizeof($arr); $i++){
echo getCharAt($i);
}
echo "\n";
}
function rotateLeft($steps)
{
global $head;
$head += $steps;
}
function rotateRight($steps)
{
global $head;
$head -= $steps;
}
function move($from, $to) {
global $arr;
if ($to =$to; $i--){
$newChar = getCharAt($i);
setCharAt($i, $char);
setCharAt($i+1, $newChar);
}
}
else {
$char = getCharAt($from);
for ($i = $from+1; $i<=$to; $i++){
$newChar = getCharAt($i);
setCharAt($i, $char);
setCharAt($i-1, $newChar);
}
}
}
function rotatePos($letter) {
global $arr, $head;
$index = 0;
for ($i = 0; $i = 4) {
$index += 1;
}
rotateRight($index+1);
}
function getLines() {
$f = fopen("../day21.txt", "r");
$lines = array();
while (($buffer = fgets($f)) !== false) {
$lines[] = trim($buffer);
}
fclose($f);
return $lines;
}
function processLine($line) {
$words = explode(" ", $line);
if($words[0] == "swap" && $words[1] =="position"){
swapPos($words[2], $words[5]);
}
if($words[0] == "swap" && $words[1] =="letter"){
swapLetters($words[2], $words[5]);
}
if($words[0] == "rotate" && $words[1] =="left"){
rotateLeft($words[2]);
}
if($words[0] == "rotate" && $words[1] =="right"){
rotateRight($words[2]);
}
if($words[0] == "rotate" && $words[1] =="based"){
rotatePos($words[6]);
}
if($words[0] == "reverse"){
reverse($words[2], $words[4]);
}
if($words[0] == "move"){
move($words[2], $words[5]);
}
}
$lines = getLines();
foreach($lines as $line){
processLine($line);
}
printArray();
?>
This was my first foray in PHP in quite some time. It was a bit more verbose than I remembered, but I still got this one relatively easy.
The main loop was easy, as it mostly took things line by line by line, and then chose a transformation based on the text.
Most transformations are straight forward. I keep a global array and head pointer, along with a way to convert indices, get characters and set characters in the array.
$head = 0;
$arr = array("a", "b", "c", "d", "e", "f", "g", "h");
function convertIndex($index){
global $arr, $head;
$newIndex = $index+$head;
while($newIndex < 0){
$newIndex += sizeof($arr);
}
return $newIndex%sizeof($arr);
}
function getCharAt($index)
{
global $arr, $head;
$newIndex =convertIndex($index);
return $arr[$newIndex];
}
function setCharAt($index, $value)
{
global $arr, $head;
$arr[convertIndex($index)] = $value;
}
Swapping based on positions and swapping based on letters are pretty straight forward
function swapPos($pos1, $pos2) {
$tmp1 = getCharAt($pos1);
$tmp2 = getCharAt($pos2);
setCharAt($pos1, $tmp2);
setCharAt($pos2, $tmp1);
}
function swapLetters($letter1, $letter2) {
global $arr;
$index1 = array_search($letter1, $arr);
$index2 = array_search($letter2, $arr);
$arr[$index2] = $letter1;
$arr[$index1] = $letter2;
}
Reversing and Rotating were also pretty easy.
function reverse($pos1, $pos2) {
for ($i = $pos1, $j=$pos2; $i < $j; $i++, $j--){
swapPos($i, $j);
}
}
function rotateLeft($steps)
{
global $head;
$head += $steps;
}
function rotateRight($steps)
{
global $head;
$head -= $steps;
}
Once we get into moving (removing from one index and inserting in the other index), it took me a little while longer to get this. I treat moving differently based on which direction I’m going to, and then I effectively “bubble” the values to the appropriate position. I originally tried to do array slicing and recombining, but my wonky index recalculations made it tricky.
function move($from, $to) {
global $arr;
if ($to =$to; $i--){
$newChar = getCharAt($i);
setCharAt($i, $char);
setCharAt($i+1, $newChar);
}
}
else {
$char = getCharAt($from);
for ($i = $from+1; $i<=$to; $i++){
$newChar = getCharAt($i);
setCharAt($i, $char);
setCharAt($i-1, $newChar);
}
}
}
Lastly, I worked on the rotate based on the position of a letter. I pretty much searched for the letter in my array, then figured out how many rotations needed to happen.
function rotatePos($letter) {
global $arr, $head;
$index = 0;
for ($i = 0; $i = 4) {
$index += 1;
}
rotateRight($index+1);
}
