one function

src/one_function_to_rule_them_all.clj

@@ -1,43 +1,196 @@
 (ns one-function-to-rule-them-all)
 
+;; Write the function (concat-elements a-seq) that takes a sequence of sequences
+;; and concatenates them together with concat.
+;; Don’t use apply to implement this function.
+;; (concat-elements [])            ;=> ()
+;; (concat-elements [[1 2]])       ;=> (1 2)
+;; (concat-elements [[1 2] [3 4]]) ;=> (1 2 3 4)
 (defn concat-elements [a-seq]
-  :-)
+  (reduce concat [] a-seq))
+
+;; Write the function (str-cat a-seq) that takes a sequence of strings and catenates
+;; them with one space character between each.
+;; (str-cat ["I" "am" "Legend"])  ;=> "I am Legend"
+;; (str-cat ["I" "am" "back"])    ;=> "I am back"
+;; (str-cat ["more" " " "space"]) ;=> "more   space"
+;; (str-cat [])                   ;=> ""
 
 (defn str-cat [a-seq]
-  :-)
+  (if (empty? a-seq)
+    ""
+    (reduce
+      (fn [a b] (str a " " b))
+      a-seq)))
+
+;; Write the function (my-interpose x a-seq) that places x between every element of a-seq.
+;; Keep in mind how conj works for vectors.
+;; (my-interpose 0 [1 2 3])               ;=> (1 0 2 0 3)
+;; (my-interpose "," ["I" "me" "myself"]) ;=> ("I" "," "me" "," "myself")
+;; (my-interpose :a [1])                  ;=> (1)
+;; (my-interpose :a [])                   ;=> ()
 
 (defn my-interpose [x a-seq]
-  [:-])
+  (if (<= (count a-seq) 1)
+    a-seq
+    (butlast
+      (reduce
+        (fn [a b] (conj a b x))
+        []
+        a-seq))))
 
+;; Write the function (my-count a-seq) that returns the length of a sequence.
+;; Do not use count in your implementation.
+;; (my-count [])      ;=> 0
+;; (my-count [1 2 3]) ;=> 3
+;; (my-count [1])     ;=> 1
 (defn my-count [a-seq]
-  :-)
+  (reduce
+    (fn [count _] (inc count))
+    0
+    a-seq))
 
+;; Write the function (my-reverse a-seq) that reverses a sequence.
+;; (my-reverse [1 2 3]) ;=> (3 2 1)
+;; (my-reverse [1 2])   ;=> (2 1)
+;; (my-reverse [])      ;=> ()
 (defn my-reverse [a-seq]
-  [:-])
+  (reduce
+    (fn [a b] (conj a b))
+    '()
+    a-seq))
 
+;; Write the function (min-max-element a-seq) that returns the maximal and minimal elements of a-seq
+;; in a vertor like [min max].
+;; (min-max-element [2 7 3 15 4]) ;=> [2 15]
+;; (min-max-element [1 2 3 4])    ;=> [1 4]
+;; (min-max-element [1])          ;=> [1 1]
+;; (min-max-element [])
 (defn min-max-element [a-seq]
-  [:-])
+  (reduce
+    (fn [result element]
+      [(min (first result) element)
+       (max (last result)  element)])
+    [Double/POSITIVE_INFINITY, Double/NEGATIVE_INFINITY]
+    a-seq))
 
+;; Write the function (insert sorted-seq n) that adds the number n into a sorted sequence of number.
+;; The ordering of the sequence must be preserved.
+;; You don’t need to use reduce for this, and you probably don’t want to.
+;; (insert [] 2)      ;=> (2)
+;; (insert [1 3 4] 2) ;=> (1 2 3 4)
+;; (insert [1] 2)     ;=> (1 2)
 (defn insert [sorted-seq n]
-  [:-])
+  (let [smaller (take-while (fn [element] (< element n)) sorted-seq)
+        greater (drop (count smaller) sorted-seq)]
+    (concat smaller [n] greater)))
 
+;; Now implement (insertion-sort a-seq) using reduce and the function insert.
+;; (insertion-sort [2 5 3 1]) ;=> (1 2 3 5)
+;; (insertion-sort [1 2])     ;=> (1 2)
 (defn insertion-sort [a-seq]
-  [:-])
+  (reduce
+    insert
+    []
+    a-seq))
 
+;; Write the fuction (parity a-seq) that picks into a set those elements of a-seq that occur odd number of time.
+;; (parity [:a :b :c])    ;=> #{:a :b :c}
+;; (parity [:a :a :b :b]) ;=> #{}
+;; (parity [1 2 3 1])     ;=> #{2 3}
 (defn parity [a-seq]
-  [:-])
+  (let [toggle (fn [a-set elem]
+                 (if (contains? a-set elem)
+                   (disj a-set elem)
+                   (conj a-set elem)))]
+    (reduce toggle #{} a-seq)))
+
+;; Write the function minus that takes one or two parameters.
+;; If given a one parameter x, it returns −x.
+;; If given to parameters x and y, it returns x−y.
+;; (minus 2)   ;=> -2
+;; (minus 4 3) ;=> 1
+(defn minus
+  ([x] (- x))
+  ([x y] (- x y)))
+
+
+;; Write the function count-params that accepts any number of parameters and returns how many it was called with.
+;; You need only a one definition for this.
+;; (count-params)            ;=> 0
+;; (count-params :a)         ;=> 1
+;; (count-params :a 1 :b :c) ;=> 4
+(defn count-params [& params]
+  (count params))
+
+;; Write the function my-* that takes any number of parameters.
+;; If no parameters are given, return 1
+;; If one parameter x is given, return x.
+;; If two parameters x and y are given, return xy.
+;; If more than two parameters x, y, …… are given, return their product
+;; You are free to use *, but not apply.
+;; (my-*)           ;=> 1
+;; (my-* 4 3)       ;=> 12
+;; (my-* 1 2 3 4 5) ;=> 120
+(defn my-*
+  ([] 1)
+  ([x] x)
+  ([x y] (* x y))
+  ([x y & more]
+   (reduce my-* (my-* x y) more)))
+
+;; Remember the function pred-and that you implemented in Predicates? Write a new definition for it that works for any
+;; amount of parameters.
+;; If no parameters are given, return a predicate that always returns true.
+;; If only one predicate p is given, return p.
+;; If two predicates are given, return a predicate that returns true if both of them return true and false otherwise.
+;; If more than two predicates are given, return a predicate that returns true only if all of the predicates return
+;; true and false otherwise.
+;; (filter (pred-and) [1 0 -2])                    ;=> (1 0 -2)
+;; (filter (pred-and pos? odd?) [1 2 -4 0 6 7 -3]) ;=> (1 7)
+;; (filter (pred-and number? integer? pos? even?)
+;;         [1 0 -2 :a 7 "a" 2])                    ;=> (0 2)
+(defn pred-and
+  ([]
+   (fn [x] true))
+  ([pred1] pred1)
+  ([pred1 pred2]
+   (fn [x] (and (pred1 x) (pred2 x))))
+  ([pred1 pred2 & more]
+   (reduce pred-and (pred-and pred1 pred2) more)))
+
+
+;; Write the function my-map that works just like standard map. It takes one or more sequences and a
+;; function f that takes as many parameters as there are sequences.
+;; (my-map inc [1 2 3 4])                  ;=> (2 3 4 5)
+;; (my-map + [1 1 1] [1 1 1] [1 1 1])      ;=> (3 3 3)
+;; (my-map vector [1 2 3] [1 2 3] [1 2 3]) ;=> ((1 1 1) (2 2 2) (3 3 3))
 
-(defn minus [x]
-  :-)
+(defn foo [f seq-of-seqs]
+  (reduce
+    (fn[res a-seq] (conj res (f a-seq)))
+    []
+    seq-of-seqs))
 
-(defn count-params [x]
-  :-)
+(defn firsts [a-seq]
+  (foo first a-seq))
 
-(defn my-* [x]
-  :-)
+(defn rests [a-seq]
+  (foo rest a-seq))
 
-(defn pred-and [x]
-  (fn [x] :-))
+(defn rearrange [a-seq]
+  (cond
+    (= 0 (count (first a-seq))) []
+    (= 1 (count (first a-seq))) [(firsts a-seq)]
+    :else (cons
+            (firsts a-seq)
+            (rearrange (rests a-seq)))))
 
-(defn my-map [f a-seq]
-  [:-])
+(defn my-map [f & seq-of-seqs]
+  (reduce
+    (fn [result a-seq]
+      (do
+        (println result a-seq)
+        (conj result (apply f a-seq))))
+    []
+    (rearrange seq-of-seqs)))