Identifying Moveable Positions in 2D Arrays with PHP | CodeSignal Learn

Identifying Moveable Positions in 2D Arrays with PHP | CodeSignal Learn

Introduction

Hello, and welcome, code explorer! Today's journey takes us through the intricate paths within a 2-dimensional array, often likened to a game board. Our mission is to identify ideal spots for game piece placement. Sounds like an adventure, doesn't it? Let's embark!

Task Statement

Visualize a chessboard in the form of a 2D array, where each cell could be marked'E' for empty or'P' for a piece. Our quest involves summoning a PHP function named findPositions() . Upon examining this 2D array, this function identifies all the spots where a new piece could be placed so that it can move to another empty cell in one move. The catch is that a piece can move only to an immediately neighboring cell directly above, below, to the left, or right, but not diagonally. Consider this 4x4 board, for instance: P E E P E P E P P E P P P E P E The function should output the following pairs representing positions: (0, 1), (0, 2), (1, 2), (2, 1), (3, 1) . This output represents the positions where a new piece can fit perfectly and then be able to move in the next turn.

Solution Building: Step 1

Solution Building: Step 2

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Stepping right into action, we start with an empty positions array to help us log the sought-after positions. Understanding the dimensions of our "board" paves the way for defining boundaries in our exploration mission. In PHP, we determine the size of a 2D array using the count() function.

Using an array is crucial here because we don't know beforehand how many positions will be found. An array in PHP is dynamic and can resize itself to accommodate any number of elements, making it a perfect choice for storing an unknown number of positions.

PHP

function findPositions($board) {
    $positions = array();

    $rows = count($board);
    $cols = count($board[0]); 
    // Further exploration follows

With our boundary map, we begin our expedition across the board. We use two nested for loops to do this, traversing the entire board one cell at a time.

PHP

function findPositions($board) {
    $positions = array();

    $rows = count($board);
    $cols = count($board[0]);

    for ($i = 0; $i < $rows; $i++) {
        for ($j = 0; $j < $cols; $j++) {
            // ensuing exploration

Solution Building: Step 3

What's the plan for each cell, you ask? While exploring each cell, our trusty PHP code inspects if the cell is empty. If confirmed, it then peeks into the neighbors in the up, down, left, and right directions. If another vacant cell ('E') is spotted, we jot down the main cell's position in our positions array. PHP<?php function findPositions($board) { $positions = array(); $rows = count($board); $cols = count($board[0]); for ($i = 0; $i < $rows; $i++) { for ($j = 0; $j < $cols; $j++) { if ($board[$i][$j] === 'E') { if (($i > 0 && $board[$i - 1][$j] === 'E') || ($i < $rows - 1 && $board[$i + 1][$j] === 'E') || ($j > 0 && $board[$i][$j - 1] === 'E') || ($j < $cols - 1 && $board[$i][$j + 1] === 'E')) { $positions[] = array($i, $j); } } } } return $positions; } $board = array( array('P', 'E', 'E', 'P'), array('E', 'P', 'E', 'P'), array('P', 'E', 'P', 'P'), array('P', 'E', 'P', 'E') ); $positions = findPositions($board); foreach ($positions as $pos) { echo "(" . $pos[0] . ", " . $pos[1] . ")\n"; } // The output will be: // (0, 1) // (0, 2) // (1, 2) // (2, 1) // (3, 1)