Add Dijkstra in PowerShell (TheRenegadeCoder#4854)

Author: rzuckerm

archive/p/powershell/Dijkstra.ps1

@@ -0,0 +1,143 @@
+function Show-Usage() {
+    Write-Host "Usage: please provide three inputs: a serialized matrix, a source node and a destination node"
+    Exit(1)
+}
+
+function Parse-IntList([string]$Str) {
+    @($Str.Split(",") | ForEach-Object { [int]::Parse($_) })
+}
+
+function Test-Inputs([array]$Weights, [int]$NumVertices, [int]$Src, [int]$Dest) {
+    # Verify number of weights is a square, weights are non-negative, any non-zero weight, and source
+    # destination are valid
+    $WeightMeasurements = $Weights | Measure-Object -Minimum -Maximum
+    ($Weights.Length -eq ($NumVertices * $NumVertices) -and
+        $WeightMeasurements.Minimum -ge 0 -and
+        $WeightMeasurements.Maximum -gt 0 -and
+        $Src -ge 0 -and $Src -lt $NumVertices -and
+        $Dest -ge 0 -and $Dest -lt $NumVertices)
+}
+
+class NodeItem {
+    [int]$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])
+            }
+        }
+    }
+
+    $nodes
+}
+
+class DijkstraItem {
+    [int]$Prev = -1
+    [int]$Dist = [int]::MaxValue
+}
+
+# Source: https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm#Pseudocode
+function Invoke-Dijkstra([Node[]]$Graph, [int]$Src) {
+    # Initialize distances to infinite and previous vertices to undefined
+    $numVertices = $Graph.Length
+    $results = 0..($numVertices - 1) | ForEach-Object { [DijkstraItem]::new() }
+
+    # Indicate all nodes unvisited
+    $q = [Collections.Generic.HashSet[int]](0..($numVertices - 1))
+
+    # Set source vertex distance to 0
+    $results[$Src].Dist = 0
+
+    # While there are unvisited nodes
+    while ($q.Count) {
+        # Pick a vertex u with minimum distance from unvisited nodes
+        $u = Find-MinDistIndex $q $results
+
+        # Indicate vertex u visited
+        [void]$q.Remove($u)
+
+        # For each unvisited neighbor v of vertex u
+        foreach ($node in $Graph[$u].Children) {
+            $v = $node.Index
+            if ($v -in $q) {
+                # Get trial distance
+                $alt = $results[$u].Dist + $node.Weight
+
+                # If trial distance is smaller than distance v, update distance to v and
+                # previous vertex of v
+                if ($alt -lt $results[$v].Dist) {
+                    $results[$v].Dist = $alt
+                    $results[$v].Prev = $u
+                }
+            }
+        }
+    }
+
+    $results
+}
+
+function Find-MinDistIndex([Collections.Generic.HashSet[int]]$q, [DijkstraItem[]]$results) {
+    $minDist = [int]::MaxValue
+    $minIndex = -1
+    for ($v = 0; $v -lt $results.Length; $v++) {
+        if ($v -in $q -and $results[$v].Dist -lt $minDist) {
+            $minDist = $results[$v].Dist
+            $minIndex = $v
+        }
+    }
+
+    $minIndex
+}
+
+if ($args.Length -lt 3 -or -not $args[0]) {
+    Show-Usage
+}
+
+try {
+    $weights = Parse-IntList $args[0]
+    $src = [int]::Parse($args[1])
+    $dest = [int]::Parse($args[2])
+} catch {
+    Show-Usage
+}
+
+
+$numVertices = [int][Math]::Floor([Math]::Sqrt($weights.Length))
+if (-not (Test-Inputs $weights $numVertices $src $dest)) {
+    Show-Usage
+}
+
+# Create graph from weights
+$graph = Create-Graph $weights $numVertices
+
+# Run Dijkstra's algorithm on graph and show distance to destination
+$results = Invoke-Dijkstra $graph $src
+Write-Output $results[$dest].Dist