Minimum Spanning Tree in Php

Welcome to the Minimum Spanning Tree in Php page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

<?php
function usage()
{
    exit("Usage: please provide a comma-separated list of integers");
}

function parse_int($str_value)
{
    // Remove leading and trailing spaces
    $str_value = trim($str_value);

    // Make sure all digits
    if (preg_match("/[+-]?^\d+$/", $str_value) === FALSE)
    {
        return FALSE;
    }

    // Make sure valid integer
    if (
        filter_var(
            $str_value,
            FILTER_VALIDATE_INT,
            array(
                'options' => array(
                    'decimal' => TRUE,
                    'min_range' => PHP_INT_MIN,
                    'max_range' => PHP_INT_MAX
                )
            )
        ) === FALSE
    )
    {
        return FALSE;
    }

    return intval($str_value);
}

function parse_int_array($str_values)
{
    $str_array = explode(",", $str_values);
    $values = array();
    foreach ($str_array as $str_value)
    {
        $value = parse_int($str_value);
        if ($value === FALSE)
        {
            return FALSE;
        }

        array_push($values, $value);
    }

    return $values;
}

function create_graph($weights, $num_vertices)
{
    // Initialize nodes
    $nodes = array_map(
        function ($id) { return new Node($id); },
        range(0, $num_vertices - 1)
    );

    // Get neighbors for this node based on weights
    $index = 0;
    for ($row = 0; $row < $num_vertices; $row++)
    {
        for ($col = 0; $col < $num_vertices; $col++, $index++)
        {
            if ($weights[$index] > 0)
            {
                $nodes[$row]->add_child($col, $weights[$index]);
            }
        }
    }

    return $nodes;
}

class Node
{
    public $index;
    public $children;

    public function __construct($index)
    {
        $this->index = $index;
        $this->children = array();
    }

    public function add_child($index, $weight)
    {
        array_push($this->children, new NodeItem($index, $weight));
    }
}

class NodeItem
{
    public $index;
    public $weight;

    public function __construct($index, $weight)
    {
        $this->index = $index;
        $this->weight = $weight;
    }
}

// Prim's Minimum Spanning Tree (MST) Algorithm based on C implementation of
// https://www.geeksforgeeks.org/prims-minimum-spanning-tree-mst-greedy-algo-5/
function prim_mst(&$graph)
{
    $num_vertices = count($graph);

    // Array to store constructed MST. Indicate no parents yet
    $parents = array_fill(0, $num_vertices, -1);

    // Key values used to pick minimum weight edge. Initialize to infinity
    $keys = array_fill(0, $num_vertices, PHP_INT_MAX);

    // Indicate nothing in MST yet
    $mst_set = array_fill(0, $num_vertices, FALSE);

    // Include first vertex in MST
    $keys[0] = 0;

    // The MST will include all vertices
    for ($i = 1; $i < $num_vertices; $i++)
    {
        // Pick index of the minimum key value not already in MST
        $u = find_min_key($keys, $mst_set);

        // Add picked vertex to MST
        $mst_set[$u] = TRUE;

        // Update key values and parent indices of picked adjacent
        // vertices. Only consider vertices not yet in MST
        foreach ($graph[$u]->children as $child)
        {
            $v = $child->index;
            $graph_value = $child->weight;
            if (!$mst_set[$v] && $graph_value < $keys[$v])
            {
                $parents[$v] = $u;
                $keys[$v] = $graph_value;
            }
        }
    }

    // Construct MST information to return, skipping over root
    $mst = array();
    for ($i = 1; $i < $num_vertices; $i++)
    {
        array_push($mst, new MSTItem($parents[$i], $i, $keys[$i]));
    }

    return $mst;
}

class MSTItem
{
    public $src_index;
    public $dest_index;
    public $weight;

    function __construct($src_index, $dest_index, $weight)
    {
        $this->src_index = $src_index;
        $this->dest_index = $dest_index;
        $this->weight = $weight;
    }
}

// Find vertex with minimum key values not already in MST
function find_min_key($keys, $mst_set)
{
    $min_value = PHP_INT_MAX;
    $min_index = -1;
    foreach ($keys as $v => $key_value)
    {
        if ($key_value < $min_value && !$mst_set[$v])
        {
            $min_value = $key_value;
            $min_index = $v;
        }
    }

    return $min_index;
}

// Get total MST weight
function get_total_mst_weight($mst)
{
    return array_sum(
        array_map(
            function ($mst_item) { return $mst_item->weight; },
            $mst
        )
    );
}

// Exit if too few arguments
if (count($argv) < 2)
{
    usage();
}

// Parse 1st argument. Exit if invalid
$weights = parse_int_array($argv[1]);
if ($weights === FALSE)
{
    usage();
}

// Exit if number of weight is not a square
$num_weights = count($weights);
$num_vertices = round(sqrt($num_weights));
if ($num_weights != $num_vertices * $num_vertices)
{
    usage();
}

// Create graph from weights
$graph = create_graph($weights, $num_vertices);

// Get MST using Prim's algorithm
$mst = prim_mst($graph);

// Calculate total weight of MST and display
$total_weight = get_total_mst_weight($mst);
echo "${total_weight}\n";

Minimum Spanning Tree in Php was written by:

• rzuckerm

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

No 'How to Implement the Solution' section available. Please consider contributing.

How to Run the Solution

No 'How to Run the Solution' section available. Please consider contributing.