Minimum Spanning Tree in Powershell

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

Current Solution

function Show-Usage() {
    Write-Host "Usage: please provide a comma-separated list of integers"
    Exit(1)
}

function Parse-IntList([string]$Str) {
    @($Str.Split(",") | ForEach-Object { [int]::Parse($_) })
}

class NodeItem {
    [int]$Index
    [int]$Weight

    NodeItem([int]$index, [int]$weight) {
        $this.Index = $index
        $this.Weight = $weight
    }
}

class Node {
    [int]$Index
    [NodeItem[]]$Children

    Node([int]$index) {
        $this.Index = $index
        $this.Children = @()
    }

    [void] AddChild([int]$index, [int]$weight) {
        $this.Children += [NodeItem]::new($index, $weight)
    }
}

function Create-Graph([array]$Weights, [int]$NumVertices) {
    # Initialize nodes
    $nodes = 0..($NumVertices - 1) | ForEach-Object { [Node]::new($_) }

    # Get neighbors for this node based on weights
    $index = 0
    for ($row = 0; $row -lt $NumVertices; $row++) {
        for ($col = 0; $col -lt $NumVertices; ($col++), ($index++)) {
            if ($Weights[$index] -gt 0) {
                $nodes[$row].AddChild($col, $Weights[$index])
            }
        }
    }

    $nodes
}

class MstItem {
    [int]$SrcIndex
    [int]$DestIndex
    [int]$Weight

    MstItem([int]$srcIndex, [int]$destIndex, [int]$weight) {
        $this.SrcIndex = $srcIndex
        $this.DestIndex = $destIndex
        $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 Invoke-PrimMst([Node[]]$Graph) {
    $numVertices = $Graph.Length

    # Array to store constructed MST. Indicate no parents yet
    $parents = @(-1) * $numVertices

    # Key values used to pick minimum weight edge. Initialize to infinity
    $keys = @([int]::MaxValue) * $numVertices

    # Indicate nothing in MST yet
    $mstSet = @($false) * $numVertices

    # Include first vertex in MST
    $keys[0] = 0

    # The MST will include all vertices
    for ($i = 1; $i -lt $numVertices; $i++) {
        # Pick index of the minimum key value not already in MST
        $u = Find-MinKey $keys $mstSet

        # Add picked vertex to MST
        $mstSet[$u] = $true

        # Update key values and parent indices of picked adjacent
        # vertices. Only consider vertices not yet in MST
        foreach ($child in $Graph[$u].Children) {
            $v = $child.Index
            $w = $child.Weight
            if (-not $mstSet[$v] -and $w -lt $keys[$v]) {
                $parents[$v] = $u
                $keys[$v] = $w
            }
        }
    }

    # Construct MST information to return, skipping over root
    @(1..($numVertices - 1) | ForEach-Object { [MstItem]::new($parents[$_], $_, $keys[$_]) })
}

function Find-MinKey([int[]]$Keys, [bool[]]$MstSet) {
    $minValue = [int]::MaxValue
    $minIndex = -1
    for ($v = 0; $v -lt $Keys.Length; $v++) {
        if ($Keys[$v] -lt $minValue -and -not $MstSet[$v]) {
            $minValue = $Keys[$v]
            $minIndex = $v
        }
    }

    $minIndex
}

function Invoke-MstTotalWeight([MstItem[]]$mst) {
    ($mst.Weight | Measure-Object -Sum).Sum
}

if ($args.Length -lt 1 -or -not $args[0]) {
    Show-Usage
}

try {
    $weights = Parse-IntList $args[0]
} catch {
    Show-Usage
}

$numVertices = [int][Math]::Floor([Math]::Sqrt($weights.Length))
if ($weights.Length -ne $numVertices * $numVertices) {
    Show-Usage
}

# Create graph from weights
$graph = Create-Graph $weights $numVertices

# Get MST using Prim's algorithm
$mst = Invoke-PrimMst $graph

# Calculate total weight of MST
$totalWeight = Invoke-MstTotalWeight $mst
Write-Output $totalWeight

Minimum Spanning Tree in Powershell 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

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