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3 files changed, 158 insertions, 0 deletions

diff --git a/ch-1.lsp b/ch-1.lsp
new file mode 100644
index 0000000000..538cf3169e
--- /dev/null
+++ b/ch-1.lsp
@@ -0,0 +1,29 @@
+(setf n 20)
+(setf seq () )
+(setf peak_eles ())
+(setf range 50)
+(make-random-state)
+
+(loop for i from 1 upto n do
+  (setf seq (cons (random range) seq))
+)
+
+(setf seq2 seq)
+
+
+(setf x (cadr seq2))
+(setf nm2 (- n 2))
+
+(loop for i from 1 upto nm2 do
+  (setf a (car seq2))
+  (setf b (caddr seq2))
+  (if (AND (< a x) (< b x)) (setf peak_eles (cons x peak_eles)) () )
+  (setf seq2 (cdr seq2) )
+  (setf x (cadr seq2) )
+  (setf l (length seq2) )
+)
+
+(setf peak_eles (reverse peak_eles))
+
+seq   ; the sequence given
+peak_eles   ; peak elements
diff --git a/ch-1.pl b/ch-1.pl
new file mode 100644
index 0000000000..a395d02ddc
--- /dev/null
+++ b/ch-1.pl
@@ -0,0 +1,34 @@
+#!/usr/bin/perl
+#
+# Perl Weekly Challenge #071 Task 1 Peak Elements
+#
+# Usage: ch-1.pl $N
+
+use strict;
+use warnings;
+
+my $N;
+my @seq = ();
+my @peak_eles = ();
+
+if ($ARGV[0]) {$N = $ARGV[0];} else {$N = 10;}
+
+for (1..$N) {
+   push @seq, 1+int(rand(50))
+}
+
+sub checkpeak {
+    my $p = $_[0];
+    if ($seq[$p-1] < $seq[$p] and $seq[$p+1] < $seq[$p]) {
+        push @peak_eles, $seq[$p];
+    }
+}
+
+for (1..$N-2) {
+    checkpeak($_);
+}
+
+print "Array: [ ", join ", ", @seq;
+print "]\n";
+print "Peak: [ ", join ", ", @peak_eles;
+print "]\n";
diff --git a/ch-2.pl b/ch-2.pl
new file mode 100644
index 0000000000..d0be12efd0
--- /dev/null
+++ b/ch-2.pl
@@ -0,0 +1,95 @@
+#!/usr/bin/perl
+# Perl Weekly Challenge 071 Task 2
+# 
+# ref: http://rosettacode.org/wiki/Linked_list#Singly-Linked_List
+#
+# Usage: ch-2.pl [ITEMS in the list] [$N]
+
+use Data::Dumper;
+use strict;
+use warnings;
+
+my @input;
+my $N;
+my @last_np1th_ref = ();
+
+@input = (5,6,3,2);
+$N = 3;
+
+if ($ARGV[0] and $ARGV[1]) {
+    $N = pop @ARGV;
+    @input = @ARGV; 
+}
+
+sub insert_after {
+    my $node = $_[0];
+    my $next = $node->{_next};
+    shift;
+    while (defined $_[0]) {
+        $node->{_next} = $_[0];
+        $node = $node->{_next};
+        shift;
+    }
+    $node->{_next} = $next;
+}
+
+sub stored_np1th_ref_from_tail {
+    push @last_np1th_ref, $_[0];
+    if ( $#last_np1th_ref > $N) {
+        shift @last_np1th_ref;
+    }
+}
+
+my $list = {value => 'HEAD'};
+
+sub insert_input {
+    for my $v (reverse @input) {          #why need reverse here? 
+        insert_after $list, { value=> $v};
+    }
+}
+
+sub print_linked_list {
+#    print "HEAD->";
+    my $node = $list->{_next};
+    print $node->{value}, "->";
+        while ($node = $node->{_next}) {
+        print $node->{value};
+        print "->"
+    }
+    print "nil";
+    print "\n";
+}
+
+insert_input;
+print_linked_list;
+
+print "The '$N'-th node counted from the tail will be deleted. \n";
+
+my $size = 0;
+my $f = $list;
+while (defined(my $x = $f->{_next})) {
+    $size++;
+    stored_np1th_ref_from_tail( \$x );
+    $f = $x;
+}
+
+sub remove_ref_as_req {
+    if ( $N > 1 ) {
+        if ($N < $size) {
+            undef ${$last_np1th_ref[1]};
+            ${$last_np1th_ref[0]}->{_next} = ${$last_np1th_ref[2]}; 
+        }
+        else {
+            undef $list->{_next};
+            $list->{_next} = ${$last_np1th_ref[1]}; 
+        }
+    }
+    else {
+        undef ${$last_np1th_ref[1]};
+        ${$last_np1th_ref[0]}->{_next} = undef; 
+    }
+}
+
+
+remove_ref_as_req;
+print_linked_list;