From 54214ae0aaae3cb686ac84818ae23d16f72d186d Mon Sep 17 00:00:00 2001
From: Fabio Scotto di Santolo <fabio.scottodisantolo@gmail.com>
Date: Fri, 5 Sep 2025 11:59:55 +0200
Subject: [PATCH] Solution exercises from P01 to P07

---
 p01.el |  9 +++++++++
 p02.el |  9 +++++++++
 p03.el |  9 +++++++++
 p04.el | 10 ++++++++++
 p05.el | 10 ++++++++++
 p06.el |  7 +++++++
 p07.el | 10 ++++++++++
 7 files changed, 64 insertions(+)
 create mode 100644 p01.el
 create mode 100644 p02.el
 create mode 100644 p03.el
 create mode 100644 p04.el
 create mode 100644 p05.el
 create mode 100644 p06.el
 create mode 100644 p07.el

diff --git a/p01.el b/p01.el
new file mode 100644
index 0000000..1dd2325
--- /dev/null
+++ b/p01.el
@@ -0,0 +1,9 @@
+;; P01 (*) Find the last box of a list
+(defun my-last (lst)
+  (cond
+   ((eq lst '()) '())
+   ((eq (cdr lst) '()) lst)
+   (t
+    (my-last (cdr lst)))))
+
+(my-last '(a b c d)) ; '(d)
diff --git a/p02.el b/p02.el
new file mode 100644
index 0000000..968cbfd
--- /dev/null
+++ b/p02.el
@@ -0,0 +1,9 @@
+;; P02 (*) Find the last but one box of a list
+(defun my-but-last (lst)
+  (cond
+   ((eq lst '()) '())
+   ((eq (cddr lst) '()) lst)
+   (t
+    (my-but-last (cdr lst)))))
+
+(my-but-last '(a b c d)) ; '(c d)
diff --git a/p03.el b/p03.el
new file mode 100644
index 0000000..b17790d
--- /dev/null
+++ b/p03.el
@@ -0,0 +1,9 @@
+;; P03 (*) Find the k'th element of a list
+(defun element-at (lst k)
+  (cond
+   ((eq lst '()) '())
+   ((eq k 1) (car lst))
+   (t
+    (element-at (cdr lst) (- k 1)))))
+
+(element-at '(a b c d) 3) ; c
diff --git a/p04.el b/p04.el
new file mode 100644
index 0000000..84f9e88
--- /dev/null
+++ b/p04.el
@@ -0,0 +1,10 @@
+;; P04 (*) Find the number of element of a list
+(defun my-length (lst)
+  (defun my-length-rec (lst res)
+    (cond
+     ((eq lst '()) res)
+     (t
+      (my-length-rec (cdr lst) (+ 1 res)))))
+  (my-length-rec lst 0))
+
+(my-length '(a b c)) ; 3
diff --git a/p05.el b/p05.el
new file mode 100644
index 0000000..8d4993a
--- /dev/null
+++ b/p05.el
@@ -0,0 +1,10 @@
+;; P05 (*) Reverse a list
+(defun my-reverse (lst)
+  (defun my-reverse-rec (lst res)
+    (cond
+     ((eq lst '()) res)
+     (t
+      (my-reverse-rec (cdr lst) (cons (car lst) res)))))
+  (my-reverse-rec lst '()))
+
+(my-reverse '(a b c)) ; '(c b a)
diff --git a/p06.el b/p06.el
new file mode 100644
index 0000000..0c118ef
--- /dev/null
+++ b/p06.el
@@ -0,0 +1,7 @@
+;; P06 (*) Find out whether a list is a palindrome.
+(defun palindrome (lst)
+  (equal lst (reverse lst)))
+
+(palindrome '(x a m a x)) ; t
+(palindrome '(a n n a))   ; t
+(palindrome '(f a b i o)) ; nil
diff --git a/p07.el b/p07.el
new file mode 100644
index 0000000..9a4a175
--- /dev/null
+++ b/p07.el
@@ -0,0 +1,10 @@
+;; P07 (**) Flatten a nested list structure.
+(defun my-flatten (l)
+  (cond
+   ((null l) nil)
+   ((atom l) (list l))
+   (t
+    (append (my-flatten (car l))
+	    (my-flatten (cdr l))))))
+
+(my-flatten '(a (b (c d) e))) ; '(a b c d e)