Number of connections

NumberOfConnections.php

<?php
/**
 * Created by PhpStorm.
 * User: adriano
 * Date: 14/11/19
 * Time: 16:37
 */

function numberOfConnections( $gridOfNodes ) {

	$nodesPreviousLine = null;
	$connections = 0;

	foreach( $gridOfNodes as $row ) {

		$nodesLine = 0;
		foreach ( $row as $line ) {
			if ( $line === 1 ) {
				$nodesLine ++;
			}
		}

		if ( $nodesPreviousLine !== null ) {
			$connections += $nodesLine * $nodesPreviousLine;
		}

		if ( $nodesLine ) {
			$nodesPreviousLine = $nodesLine;
		}
	}

	return $connections;
}

$grid = [
	[ 1, 0, 1, 1 ],
	[ 0, 1, 1, 0 ],
	[ 0, 0, 0, 0 ],
	[ 1, 0, 0, 0 ],
];

assert( 8 === numberOfConnections( $grid ) );

assert( 17 === numberOfConnections(
	[
		[ 1, 0, 1, 1, 1 ],
		[ 0, 1, 1, 0, 1 ],
		[ 0, 0, 0, 0, 1 ],
		[ 1, 0, 0, 0, 1 ],
	]
        ) );