add code to make fns non destructive - and a "test" to test this

1 files changed, 16 insertions, 1 deletions

diff --git a/challenge-100/james-smith/perl/ch-2.pl b/challenge-100/james-smith/perl/ch-2.pl
index 6ffe7fc6e3..46a05310f1 100644
--- a/challenge-100/james-smith/perl/ch-2.pl
+++ b/challenge-100/james-smith/perl/ch-2.pl
@@ -6,6 +6,15 @@ use warnings;
 use feature qw(say);
 use Test::More;
 
+## A little check to see if the sum functions are
+## non-destructive...
+my @Q = ( [1],[2,4],[6,4,9],[5,1,7,2] );
+triangle_sum_1point5_liner( @Q );
+is( triangle_sum_1point5_liner( @Q ), 8 );
+@Q = ( [1],[2,4],[6,4,9],[5,1,7,2] );
+triangle_sum( @Q );
+is( triangle_sum( @Q ), 8 );
+
 is( triangle_sum( [1],[2,4],[6,4,9],[5,1,7,2] ),  8 );
 is( triangle_sum( [3],[3,1],[5,2,3],[4,3,1,3] ),  7 );
 is( triangle_sum( [3],[3,1],[3,8,9],[4,3,1,3] ), 12 );
@@ -37,7 +46,7 @@ display_sum( [3],[6,4],[5,2,7],[9,1,8,6] );
 ## repeating until the triangle only has a single cell the answer..
 
 sub triangle_sum {
-  my @tri = @_;
+  my @tri = map{ [@{$_}] } @_;
   while(@tri>1) {
       ## Strip off base of triangle...
     my $b = pop @tri;
@@ -49,6 +58,11 @@ sub triangle_sum {
   return $tri[0][0];
 }
 
+## First thing we do is make a deep copy of @_ as this like the
+## previous function is destructive. @_ is an array of references
+## and although manipulating @_ doesn't affect the variable passed
+## in it does affect the contents of any references passed in.
+##
 ## We can convert the inner for loop into a map... and pop the value
 ## of $b in the while clause so we can simplify this down to a single
 ## one line statement, with the return just returning the last
@@ -57,6 +71,7 @@ sub triangle_sum {
 ## so not quite a 1 liner - but close enough!!
 
 sub triangle_sum_1point5_liner {
+  @_ = map{ [@{$_}] } @_; ## Deep copy as destructive..
   @{$_[-1]} = map {
     $_[-1][$_] + $b->[ $b->[$_] < $b->[$_+1] ? $_ : $_+1 ]
   } 0..@_-1 while @{$b=pop @_}>1;