PHP - how to tell if ALL adjacent elements in multidimensional array exist? - php

Question

This is a stupid small problem we had at work that a few of us have different solutions to, and we're wondering if there's a better way to do it. I'll boil it down to something really simple for the sake of example.
Say we have a multidimensional array with the below values in it. Each value is it's own element, and each row is an array.
0a00
000b
c000
In the above "array", $array[0][1] would be "a", $array[1][3] would be "b", and $array[2][0] would be "c". What we need to do, is increment all values adjacent to non-numeric values by 1. So, the array after we've incremented the values should look like the below array. The current solution we have is to first check all 4 "corners" of the array, increment the adjacent values, then check the top and bottom rows, then check the first and last columns, and finally, check all other elements. Whenever we hit a non-numeric element, we increment all other adjacent non-numeric elements by 1. This is kind of lame/cumbersome, and we know there has to be a better way. It's pretty much building a bombsweeper board in reverse, when you know where all of the bombs are.
1a21
222b
c111

Answer 1

I have in mind this simple algorithm:
function getNeighborsCount($rgData, $iX, $iY)
{
if(ord($rgData[$iX][$iY])>=ord('a') && ord($rgData[$iX][$iY])<=ord('z'))
{
return null;
}
$iResult = 0;
for($i=$iX-1; $i<=$iX+1; $i++)
{
for($j=$iY-1; $j<=$iY+1; $j++)
{
if(isset($rgData[$i][$j]) &&
ord($rgData[$i][$j])>=ord('a') &&
ord($rgData[$i][$j])<=ord('z'))
{
$iResult++;
}
}
}
return $iResult;
}
-then apply it to whole array:
$rgData = [
str_split('0a00'),
str_split('000b'),
str_split('c000')
];
for($i=0; $i<count($rgData); $i++)
{
for($j=0; $j<count($rgData[$i]); $j++)
{
if($iCount = getNeighborsCount($rgData, $i, $j))
{
$rgData[$i][$j]=$iCount;
}
}
}
-this will result with
echo(join(PHP_EOL, array_map(function($rgStr)
{
return join('', $rgStr);
}, $rgData)));
to:
1a21
222b
c111
Now, about complexity. If we have N elements, it will be O(9N) since we're iterating 9 times for each element inside function.

Answer 2

Funny little puzzle. Try the following:
$arr = array(
array(0, 'a', 0, 0),
array(0, 0, 0, 'b'),
array('c', 0, 0, 0),
);
$max_i = count($arr);
$max_j = count($arr[0]);
for ($i = 0; $i < $max_i; $i++) {
for ($j = 0; $j < $max_j; $j++) {
if (!is_int($arr[$i][$j])) {
for ($_i = $i - 1; $_i <= $i + 1; $_i++) {
for ($_j = $j - 1; $_j <= $j + 1; $_j++) {
if (($_i == $i && $_j == $j) || $_i < 0 || $_i >= $max_i || $_j < 0 || $_j >= $max_j) {
continue;
}
if (is_int($arr[$_i][$_j])) {
$arr[$_i][$_j]++;
}
}
}
}
}
}
Not sure if this is the most efficient way, but it should be shorter than what you have.