From 3cb38e50045d89ec19e2128d4ad1ca508e9e30ba Mon Sep 17 00:00:00 2001
From: Upasana <me@upasana.me>
Date: Sun, 19 Jul 2015 02:24:28 +0530
Subject: [PATCH] Solution of 100 Doors problem in Perl & Erlang

---
 .../Erlang/Sweet-kid/doors_100.erl            | 75 +++++++++++++++++++
 100_Doors_Problem/Perl/Sweet-kid/100_Doors.pl | 52 +++++++++++++
 2 files changed, 127 insertions(+)
 create mode 100644 100_Doors_Problem/Erlang/Sweet-kid/doors_100.erl
 create mode 100644 100_Doors_Problem/Perl/Sweet-kid/100_Doors.pl

diff --git a/100_Doors_Problem/Erlang/Sweet-kid/doors_100.erl b/100_Doors_Problem/Erlang/Sweet-kid/doors_100.erl
new file mode 100644
index 00000000..ce8d23ba
--- /dev/null
+++ b/100_Doors_Problem/Erlang/Sweet-kid/doors_100.erl
@@ -0,0 +1,75 @@
+-module(doors_100).
+-compile(export_all).
+-import(lists).
+
+main() ->
+    %% false represents a closed door & true represents an open door
+    Doors = lists:duplicate(100, false),
+    Result = toggle_doors( Doors, 0 ),
+    io:format("Open doors:~n"),
+    print_open_doors( Result, 1),
+    OpenDoorsIndex = [ X*X || X <- lists:seq( 1, 10) ],
+    TestPassed = test_open_doors( Result, 1, OpenDoorsIndex ),
+    if TestPassed == true ->
+            io:format("~nTest passed~n");
+       true ->
+            io:format("~nTest failed~n")
+    end.
+
+test_open_doors(_, 101, _) ->
+    true;
+
+test_open_doors(Result, CurrentIndex, OpenDoorsIndex) ->
+    IsAnOpenDoor = lists:member( CurrentIndex, OpenDoorsIndex ),
+    %% index for nth should be >=1
+    Door = lists:nth( CurrentIndex, Result ),
+    if IsAnOpenDoor == true ->
+            if Door == true ->
+                    test_open_doors( Result, CurrentIndex + 1, OpenDoorsIndex );
+               true ->
+                    io:format("test failed for ~p~n", [CurrentIndex]),
+                    false
+            end;
+       true ->
+            if Door == false ->
+                    test_open_doors( Result, CurrentIndex + 1, OpenDoorsIndex );
+               true ->
+                    io:format("test failed for ~s~n", [CurrentIndex]),
+                    false
+            end
+    end.
+
+print_list([], _) ->
+    io:format("~n");
+print_list([H|T], N) ->
+    io:format("~p ", [H]),
+    if (N rem 10) == 0 ->
+            io:format("~n"),
+            print_list(T, N+1);
+       true ->
+            print_list(T, N+1)
+    end.
+
+print_open_doors([], _) ->
+    io:format("~n");
+print_open_doors([H|T], N) ->
+    if H == true ->
+            io:format("~p ",[N]),
+            print_open_doors(T, N+1);
+       true ->
+            print_open_doors(T, N+1)
+    end.
+
+toggle_doors( Doors, 100 ) -> Doors;
+toggle_doors( Doors, Turn) ->
+    toggle_doors( toggle_doors_per_turn( Doors, 1, Turn), Turn + 1 ).
+
+toggle_doors_per_turn( Doors, Current, Turn ) ->
+    if Current*(Turn+1) > 100 ->
+            Doors;
+       true ->
+            ToggledDoors = lists:sublist( Doors, Current*(Turn + 1) - 1 ) ++
+                [ not lists:nth(  Current*(Turn + 1) , Doors) ] ++
+                lists:sublist( Doors, Current*(Turn + 1) + 1, length( Doors ) - Current*(Turn + 1) + 1 ),
+            toggle_doors_per_turn( ToggledDoors, Current + 1, Turn )
+    end.
diff --git a/100_Doors_Problem/Perl/Sweet-kid/100_Doors.pl b/100_Doors_Problem/Perl/Sweet-kid/100_Doors.pl
new file mode 100644
index 00000000..dc097cb7
--- /dev/null
+++ b/100_Doors_Problem/Perl/Sweet-kid/100_Doors.pl
@@ -0,0 +1,52 @@
+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+
+use POSIX;
+
+sub toggle_doors {
+    my ($doors, $start) = @_;
+    for( my $i = 1; ($start*$i - 1) < 100; $i++ ) {
+        $doors->[ $start*$i - 1 ] = !$doors->[ $start*$i - 1 ];
+    }
+}
+
+sub print_open_doors {
+    my ($doors) = @_;
+    print "Open doors:\n";
+    for( my $i = 0; $i < 100; $i++ ) {
+        if( $doors->[ $i ] ) {
+            print ($i + 1);
+            print " ";
+        }
+    }
+    print "\n";
+}
+
+sub test_doors {
+    my $doors = shift;
+
+    my @expected = (0) x 100 ;
+    
+    for( my $i = 1; $i <= 10; $i++ ) {
+        $expected[ ($i*$i) - 1 ] = 1;
+    }
+
+    for( my $i = 0; $i <= $#expected; $i++ ) {
+        if( $doors->[ $i ] != $expected[ $i ] ) {
+            die "test failed for index $i\n";
+        }
+    }
+
+    print "\nAll tests passed\n\n";
+}
+
+my @doors = ( 0 ) x 100;
+for( my $i = 1; $i <= 100; $i++ ) {
+    toggle_doors( \@doors, $i );
+}
+
+print_open_doors( \@doors );
+test_doors( \@doors );
+