Data commit

Task/Truncatable-primes/PowerShell/truncatable-primes.psh

@@ -0,0 +1,51 @@
+function IsPrime ( [int] $num )
+{
+    $isprime = @{}
+    2..[math]::sqrt($num) | Where-Object {
+        $isprime[$_] -eq $null } | ForEach-Object {
+        $_
+        $isprime[$_] = $true
+        for ( $i=$_*$_ ; $i -le $num; $i += $_ )
+        { $isprime[$i] = $false }
+    }
+    2..$num | Where-Object { $isprime[$_] -eq $null }
+}
+
+function Truncatable ( [int] $num )
+{
+    $declen = [math]::abs($num).ToString().Length
+    $primes = @()
+    $ltprimes = @{}
+    $rtprimes = @{}
+    1..$declen | ForEach-Object { $ltprimes[$_]=@{}; $rtprimes[$_]=@{} }
+    IsPrime $num | ForEach-Object {
+        $lastltprime = 2
+        $lastrtprime = 2
+    } {
+        $curprim = $_
+        $curdeclen = $curprim.ToString().Length
+        $primes += $curprim
+        if( $curdeclen -eq 1 ) {
+            $ltprimes[1][$curprim] = $true
+            $rtprimes[1][$curprim] = $true
+            $lastltprime = $curprim
+            $lastrtprime = $curprim
+        } else {
+            $curmod = $curprim % [math]::pow(10,$curdeclen - 1)
+            $curdiv = [math]::floor($curprim / 10)
+            if( $ltprimes[$curdeclen - 1][[int]$curmod] ) {
+                $ltprimes[$curdeclen][$curprim] = $true
+                $lastltprime = $curprim
+            }
+            if( $rtprimes[$curdeclen - 1][[int]$curdiv] ) {
+                $rtprimes[$curdeclen][$curprim] = $true
+                $lastrtprime = $curprim
+            }
+        }
+        if( ( $ltprimes[$curdeclen - 2].Keys.count -gt 0 ) -and ( $ltprimes[$curdeclen - 1].Keys.count -gt 0 ) ) { $ltprimes[$curdeclen -2] = @{} }
+        if( ( $rtprimes[$curdeclen - 2].Keys.count -gt 0 ) -and ( $rtprimes[$curdeclen - 1].Keys.count -gt 0 ) ) { $rtprimes[$curdeclen -2] = @{} }
+    } {
+        "Largest Left Truncatable Prime: $lastltprime"
+        "Largest Right Truncatable Prime: $lastrtprime"
+    }
+}