Add Convex Hull in PowerShell (TheRenegadeCoder#4859)

Author: rzuckerm

archive/p/powershell/ConvexHull.ps1

@@ -0,0 +1,98 @@
+function Show-Usage() {
+    Write-Host 'Usage: please provide at least 3 x and y coordinates as separate lists (e.g. "100, 440, 210")'
+    Exit 1
+}
+
+function Parse-IntList([string]$Str) {
+    @($Str.Split(",") | ForEach-Object { [int]::Parse($_) })
+}
+
+class Point {
+    [int]$X
+    [int]$Y
+
+    Point([int]$x, [int]$y) {
+        $this.X = $x
+        $this.Y = $y
+    }
+
+    [string] ToString() {
+        return "($($this.X), $($this.Y))"
+    }
+}
+
+function Get-Points([int[]]$X, [int[]]$Y) {
+    @(0..($X.Length - 1) | ForEach-Object { [Point]::new($X[$_], $Y[$_]) })
+}
+
+# Find Convex Hull using Jarvis' algorithm
+# Source: https://www.geeksforgeeks.org/convex-hull-using-jarvis-algorithm-or-wrapping/
+function Invoke-ConvexHull([Point[]]$Points) {
+    $n = $Points.Length
+
+    # The first point is the leftmost point with the highest y-coord in the event of a tie
+    $l = Find-LeftmostPoint $Points
+
+    # Repeat until wrapped around to first hull point
+    $p = $l
+    do {
+        # Output convex hull point
+        $Points[$p]
+
+        $q = ($p + 1) % $n
+        for ($j = 0; $j -lt $n; $j++) {
+            # If point j is more counter-clockwise, then update end point (q)
+            if ((Get-Orientation $Points[$p] $Points[$j] $Points[$q]) -lt 0) {
+                $q = $j
+            }
+        }
+
+        $p = $q
+    } while ($p -ne $l)
+}
+
+function Find-LeftmostPoint([Point[]]$Points) {
+    $leftmostPoint = [Point]::new([int]::MaxValue, [int]::MinValue)
+    $leftmostIndex = 0
+    for ($i = 0; $i -lt $Points.Length; $i++) {
+        # In the event of a tie, pick the point with the greater y-coord
+        if ($Points[$i].X -lt $leftmostPoint.X -or
+            ($Points[$i].X -eq $leftmostPoint.X -and $Points[$i].Y -gt $leftmostPoint.Y)
+        ) {
+            $leftmostPoint = $Points[$i]
+            $leftmostIndex = $i
+        }
+    }
+
+    $leftmostIndex
+}
+
+# Get orientation of three points
+#
+# 0 = points are in a line
+# > 0 = points are clockwise
+# < 0 = points are counter-clockwise
+function Get-Orientation([Point]$P, [Point]$Q, [Point]$R) {
+    ($Q.Y - $P.Y) * ($R.X - $Q.X) - ($Q.X - $P.X) * ($R.Y - $Q.Y)
+}
+
+if ($args.Length -lt 2 -or -not $args[0] -or -not $args[1]) {
+    Show-Usage
+}
+
+try {
+    $x = Parse-IntList $args[0]
+    $y = Parse-IntList $args[1]
+    if ($x.Length -ne $y.Length -or $x.Length -lt 3) {
+        Show-Usage
+    }
+} catch {
+    Show-Usage
+}
+
+# Combine values into set of points
+$points = Get-Points $X $Y
+
+# Get convex hull of points and show them
+$hullPoints = Invoke-ConvexHull $points
+Write-Output ($hullPoints -join "`n")