[lang] Reorganize language learning archive

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diff --git a/thinkperl6/draft.p6 b/thinkperl6/draft.p6
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-#!/usr/bin/env perl6
-# Exercise 2.2.1
-sub sphere-volume(Numeric(Cool) $r) { 4/3 * π * $r³ }
-#put sphere-volume('5');
-
-# Exercise 3.1
-# Notice the operator precedence
-sub rjust(Str $str, Int $width = 70) { ' ' x $width - $str.chars ~ $str }
-#put rjust("Larry Wall", 80);
-
-# Exercise 3.2
-sub print-twice($str) {
-    put $str;
-    put $str
-}
-sub do-twice(&code, $arg) {
-    code $arg;
-    code $arg
-}
-#do-twice(&print-twice, "What's up doc");
-sub do-four(&code, $arg) { do-twice { do-twice &code, $_ }, $arg }
-
-# Exercise 3.3
-sub grid(Int $rows=2, Int $cols=2, Int $side=4) {
-    (('+' for 0..$cols).join((' ' for 0..$side).join('-'))~"\n" for 0..$rows)
-    .join((('|' for 0..$cols).join(' ' x $side*2 + 1)~"\n") x $side)
-}
-#print grid(4, 4);
-
-# Exercise 4.2
-sub check-fermat(Int $a, Int $b, Int $c, Int $n) {
-    return if $n <= 2;
-    if $a**$n + $b**$n == $c**$n {
-        put "Holy smokes, Fermat was wrong!"
-    } else {
-        put "No, that doesn't work."
-    }
-}
-
-# Exercise 4.3
-sub is-triangle($a, $b, $c) { ([-] reverse sort $a, $b, $c) < 0 }
-
-# Exercise 4.4
-sub fibonacci(Int $n, Int $a = 0, Int $b = 1) {
-    return $a if $n <= 0; #put $a;
-    fibonacci $n - 1, $b, $a + $b
-}
-#put fibonacci 20;
-
-sub hypotenuse($a, $o) { sqrt $a² + $o² }
-#put hypotenuse 3, 4;
-
-# Exercise 5.2
-multi ack(0, Int $n) { $n + 1 }
-multi ack(Int $m where * > 0, 0) { ack $m - 1, 1 }
-multi ack(Int $m where * > 0, Int $n where * > 0) {
-    ack $m - 1, ack($m, $n - 1)
-}
-#put ack 3, 4;
-
-# Exercise 5.3
-sub is-palindrome(Str $str) { $str eq $str.flip }
-
-# Exercise 5.4
-sub is-power-of($a, $b) { { $_ == .Int }(log $a, $b) }
-
-# Exercise 5.5: gcd is a built-in operator
-
-# Exercise 6.1
-sub my-sqrt($a, $epsilon = 0.000_000_1, $x = $a) {
-    return $x if abs $x² - $a < $epsilon;
-    my-sqrt $a, $epsilon, ($x + $a/$x) / 2
-}
-
-# Exercise 6.2
-sub factorial(Int $n) { [*] 1..$n }
-sub estimate-pi {
-    my $factor = 2 * 2.sqrt / 9801;
-    sub Srinivasa-Ramanujan($k = 1, $current = 1103, $result = 1103) {
-        my $next = factorial($k * 4) * (1103 + $k*26390)
-                   / factorial($k)⁴ / 396**($k*4);
-        return $result + $next if $factor * $next < 10**-15;
-        Srinivasa-Ramanujan $k + 1, $next, $result + $next;
-    }
-    1 / $factor / Srinivasa-Ramanujan
-}
-#put abs estimate-pi() - pi;
-
-sub ducks { map * ~ 'ack' , flat('J'..'N', 'Ou', 'P', 'Qu') }
-#put ducks;
-
-sub count(Str $string, Str $substr, Int $index = 0, Int $result = 0) {
-    my $i = index $string, $substr, $index;
-    return $result unless defined $i;
-    count $string, $substr, $i + 1, $result + 1
-}
-#put count 'banana', 'na';
-
-sub bubble-sort(@seq is copy) {
-    my $done;
-    repeat {
-        $done = True;
-        for ^@seq.end -> $i {
-            if @seq[$i] > @seq[$i+1] {
-                @seq[$i, $i + 1] .= reverse
-                $done = False
-            }
-        }
-    } until $done;
-    @seq
-}
-#put bubble-sort <4 2 6 5 3 9 1>;
-
-sub select-sort(@seq is copy) {
-    for ^@seq.end -> $i {
-        for $i..@seq.end -> $j {
-            @seq[$i, $j] .= reverse if @seq[$i] > @seq[$j]
-        }
-    }
-    @seq
-}
-#put select-sort <4 2 6 5 3 9 1>;
-
-sub insert-sort(@seq is copy) {
-    for 1..@seq.end -> $i {
-        loop (my $j = $i; $j and @seq[$j] < @seq[$j - 1]; $j--) {
-            @seq[$j, $j - 1] .= reverse
-        }
-    }
-    @seq
-}
-#put insert-sort <4 2 6 5 3 9 1>;
-
-# Some simple regexes
-#put $/ if "π ≈ $(π)" ~~ /\d**10/;
-#put $/ if '1234567890' ~~ /^ <[0..7]>+ $/;
-#put $/ if ' Hello, World!' ~~ /\w+/;
-#put $/ if 'qaz asdf zxcv' ~~ /<< a \w*/;
-#put $/ if 'hmmm ooer' ~~ /<< <[aeiou]> \w*/;
-#put $/ if '0621323 0612345678- 0701234567' ~~ /<< 0 <[67]> \d**8 >>/;
-#put $/ if 'hMmM OoEr' ~~ /:i << <[aeiou]> \w*/;
-#put $/ if 'hmmm ooer' ~~ /(\w)$0/;
-#put $1 if 'hmmm ooer' ~~ /(\w) $0 .* ((\w) $0)/;
-
-sub YYYY-MM-DD(Str $string) {
-    "$0-$1-$2" if $string ~~ /<< (\d\d\d\d) \- (\d\d) \- (\d\d) >>
-    <?{0 < $1 < 13 && $2 && ($1 - 2 && $2 < 31 + ($1 - 1)%7%%2 ||
-                             $2 < 29 + $0%%400 + ($0%100)*($0%%4))}>/
-}
-#put YYYY-MM-DD '986-05-19-1700-02-29-1234-11-31-01-10-2000-02-29';
-
-# Exercise 7.3
-sub rotate-ascii(Str $string, Int $rotation) {
-    $string.comb.map({ m/<[A..Z]>/ && chr(65 + ($/.ord + $rotation - 65)%26) ||
-                       m/<[a..z]>/ && chr(97 + ($/.ord + $rotation - 97)%26) ||
-                       $_ }).join
-}
-#put rotate-ascii 'cheer', 7;
-#put rotate-ascii 'melon', -10;
-#put rotate-ascii 'HAL', 1;
-
-# Exercise 8.1
-#.put if .chars > 20 for '/usr/share/dict/words'.IO.lines;
-
-# Exercise 8.2
-sub words(&predicate) { '/usr/share/dict/words'.IO.lines.grep(&predicate) }
-#.put for words({ not /<[Ee]>/ });
-
-# Exercise 8.3
-multi avoids(@letters, @forbidden) { ($_ ∉ @letters for @forbidden).all }
-multi avoids(Str $word, Str $forbidden) { avoids $word.comb, $forbidden.comb }
-sub least-forbidden(Int $n) {
-    my %avoids = [$_ => {} for 'a'..'z'];
-    for '/usr/share/dict/words'.IO.lines.map(~*.lc).unique -> $word {
-        %avoids{$_}{$word} = True unless defined index $word, $_ for 'a'..'z';
-    }
-
-    # Despacito (baby take it slow so we can last long)
-    [([∩] %avoids{$_}).elems => $_ for combinations('a'..'z', $n)].max.value
-}
-# Unless run on a supercomputer, there ain't no way
-# one has the patience to wait for it to finish.
-#say least-forbidden 5;
-
-# Exercise 8.4
-#.put for words { m:i/^ <[acefhlo]>+ $/ };
-
-# Exercise 8.5
-my @uses-all = <a e i o u y>;
-#.put for words { (defined index $^word, $_ for @uses-all).all };
-
-# Exercise 8.6
-sub is-abcdedarian(Str $word) { [lt] $word.lc.comb }
-#.put for words &is-abcdedarian;
-
-# Exercise 8.7
-#.put for words { m/(.) $0 (.) $1 (.) $2/ };
-
-# Exercise 8.8
-#.put if [.substr(2), substr($_ + 1, 1), substr($_ + 2, 1, 4), ~($_ + 4)]
-#        .map(&is-palindrome).all for 100_000..999_996;
-
-# Exercise 8.9
-sub age-reversible(Int $times) {
-    for '10'..'90' -> $car {
-        my $diff = $car - $car.flip;
-        my @reversible = grep { .flip == $_ - $diff }, $car..'99';
-        return @reversible if @reversible == $times
-    }
-}
-#put age-reversible(8)[*-3].flip;
-
-# Exercise 9.1
-multi nested-sum(Numeric $number) { $number }
-multi nested-sum(@array) { @array.map(&nested-sum).sum }
-#put nested-sum [1, 2, [3, 4], [5, [6, 7]], [[8], [9, [10]]]];
-
-# Exercise 9.2
-#put [\+] 1..4;
-
-# Exercise 9.5
-#put [≤] (1, 2, 2);
-#put [≤] (1, 2, 1);
-
-# Exercise 9.6
-sub is-anagram(Str $this, Str $that) { $this.comb.sort ~~ $that.comb.sort }
-#put is-anagram 'this', 'shit';
-
-# Exercise 9.7
-sub has-duplicates(@array) { @array.unique != @array }
-#put has-duplicates <o o e r>;
-
-# Exercise 9.8
-sub birthday-paradox(Int $n, Int $T) {
-    sum(map { has-duplicates map { 365.25.rand.Int }, ^$n }, ^$T) / $T
-}
-#put birthday-paradox 23, 10000;
-
-# Exercise 9.10
-sub bisect(@a, $x, Int $low = 0, Int $high = @a.elems) {
-    return unless $low < $high;
-    my $mid = ($low + $high) div 2;
-    given @a[$mid] cmp $x {
-        when Less { bisect @a, $x, $mid + 1, $high }
-        when Same { $mid }
-        when More { bisect @a, $x, $low, $mid }
-    }
-}
-
-# Exercise 9.11
-#my @words = '/usr/share/dict/words'.IO.lines;
-#put "$_ $(.flip)" if /^(.)$0*$/ ^ defined bisect @words, .flip for @words;
-
-# Exercise 9.12
-sub interlock(Str $word, @words) {
-    my ($evens, $odds);
-    for $word.comb -> $even, $odd = '' {
-        $evens ~= $even;
-        $odds ~= $odd
-    }
-    bisect(@words, $evens).defined && bisect(@words, $odds).defined
-}
-#my @words = '/usr/share/dict/words'.IO.lines;
-#.put for @words.grep:{ interlock($_, @words) };
-
-# Exercise 10.3
-sub hash-duplicates(@array) {
-    my %hash;
-    for @array {
-        return True if %hash{$_};
-        %hash{$_} = True
-    }
-    False
-}
-#put hash-duplicates <o o e r>;
-
-# Exercise 10.4
-sub rotations {
-    my %words = '/usr/share/dict/words'.IO.lines.grep(/^ <[a..z]>+ $/).Set;
-    my @result;
-    for %words.keys -> $word {
-        next unless %words{$word};
-        (%words{$word}, $_) = False, $word;
-        my $virgin = True;
-        loop (tr/a..z/b..za/; $_ cmp $word; tr/a..z/b..za/) {
-            next unless %words{$_};
-            %words{$_} = False;
-            if $virgin {
-                $virgin = False;
-                @result.push([$word, $_])
-            } else {
-                @result[*-1].push($_)
-            }
-        }
-    }
-    @result
-}
-.put for rotations;