From 3ba59e2c4ac168b4a6983cb22300568b9b73fac7 Mon Sep 17 00:00:00 2001
From: 冯昶 <seaker@qq.com>
Date: Mon, 10 May 2021 18:33:06 +0800
Subject: challenge 112, raku solutions

---
 challenge-112/feng-chang/raku/ch-1.raku | 23 +++++++++++++++++++++++
 challenge-112/feng-chang/raku/ch-2.raku | 15 +++++++++++++++
 2 files changed, 38 insertions(+)
 create mode 100755 challenge-112/feng-chang/raku/ch-1.raku
 create mode 100755 challenge-112/feng-chang/raku/ch-2.raku

diff --git a/challenge-112/feng-chang/raku/ch-1.raku b/challenge-112/feng-chang/raku/ch-1.raku
new file mode 100755
index 0000000000..5175350730
--- /dev/null
+++ b/challenge-112/feng-chang/raku/ch-1.raku
@@ -0,0 +1,23 @@
+#!/bin/env raku
+
+sub MAIN(Str:D $path where * ~~ rx{^'/'}) {
+    my @dirs = $path.split(rx{'/'+}).tail(*-1);
+    @dirs.pop unless @dirs[*-1];
+    my $i = 0;
+    try {
+        while $i < @dirs.elems {
+            given @dirs[$i] {
+                when '.'  { @dirs.splice($i, 1) }
+                when '..' { @dirs.splice($i-1, 2); --$i; }
+                default   { ++$i }
+            }
+        }
+
+        CATCH {
+            $*ERR.put: 'cannot walk beyond root';
+            exit;
+        }
+    }
+
+    put '/', @dirs.join('/');
+}
diff --git a/challenge-112/feng-chang/raku/ch-2.raku b/challenge-112/feng-chang/raku/ch-2.raku
new file mode 100755
index 0000000000..f0ea1a093b
--- /dev/null
+++ b/challenge-112/feng-chang/raku/ch-2.raku
@@ -0,0 +1,15 @@
+#!/bin/env raku
+
+proto walk(UInt:D --> UInt:D) {*}
+
+multi walk(0)  { 1 }
+multi walk(1)  { 1 }
+multi walk(2)  { 2 }
+
+multi walk($n) {
+    state @memo;
+    @memo[$n] = walk($n-1) + walk($n-2) unless @memo[$n].defined;
+    @memo[$n];
+}
+
+sub MAIN(UInt:D $n) { put walk($n) }
-- 
cgit 


From 144a4fa80fbfa1d1356d05d1da1a1e7ff4cd6ba9 Mon Sep 17 00:00:00 2001
From: 冯昶 <seaker@qq.com>
Date: Mon, 10 May 2021 18:44:40 +0800
Subject: add comments

---
 challenge-112/feng-chang/raku/ch-1.raku | 10 +++++-----
 challenge-112/feng-chang/raku/ch-2.raku |  4 ++--
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/challenge-112/feng-chang/raku/ch-1.raku b/challenge-112/feng-chang/raku/ch-1.raku
index 5175350730..cf4cf08e00 100755
--- a/challenge-112/feng-chang/raku/ch-1.raku
+++ b/challenge-112/feng-chang/raku/ch-1.raku
@@ -1,20 +1,20 @@
 #!/bin/env raku
 
 sub MAIN(Str:D $path where * ~~ rx{^'/'}) {
-    my @dirs = $path.split(rx{'/'+}).tail(*-1);
-    @dirs.pop unless @dirs[*-1];
+    my @dirs = $path.split(rx{'/'+}).tail(*-1);     # put all directory names into an array, omit first empty element
+    @dirs.pop unless @dirs[*-1];                    # omit last element if it is empty
     my $i = 0;
     try {
         while $i < @dirs.elems {
             given @dirs[$i] {
-                when '.'  { @dirs.splice($i, 1) }
-                when '..' { @dirs.splice($i-1, 2); --$i; }
+                when '.'  { @dirs.splice($i, 1) }           # omit '.'
+                when '..' { @dirs.splice($i-1, 2); --$i; }  # omit '..' and its upper directory
                 default   { ++$i }
             }
         }
 
         CATCH {
-            $*ERR.put: 'cannot walk beyond root';
+            $*ERR.put: 'cannot walk beyond root';   # guard against excessive '..'s
             exit;
         }
     }
diff --git a/challenge-112/feng-chang/raku/ch-2.raku b/challenge-112/feng-chang/raku/ch-2.raku
index f0ea1a093b..b674d7b518 100755
--- a/challenge-112/feng-chang/raku/ch-2.raku
+++ b/challenge-112/feng-chang/raku/ch-2.raku
@@ -1,13 +1,13 @@
 #!/bin/env raku
 
-proto walk(UInt:D --> UInt:D) {*}
+proto walk(UInt:D --> UInt:D) {*}   # restrict dispatch pattern
 
 multi walk(0)  { 1 }
 multi walk(1)  { 1 }
 multi walk(2)  { 2 }
 
 multi walk($n) {
-    state @memo;
+    state @memo;                    # use memory to speed up counting
     @memo[$n] = walk($n-1) + walk($n-2) unless @memo[$n].defined;
     @memo[$n];
 }
-- 
cgit