# No more Easy 4Clojure

#### Jul 15, 2020

### Contents

## 4Clojure Problems

### Easy

No. 120 Sum of square of digits

```
(defn sum-of-square
[xs]
(let [make-digit (fn [n] (map #(Integer/valueOf (str %)) (String/valueOf n)))
sqr-digit (fn [n] (apply + (map #(* % %) (make-digit n))))]
(count (filter #(> (sqr-digit %) %) xs))))
(sum-of-square (range 100))
;; 50
```

No. 153 Pairwise Disjoint Sets. Given a set of sets, create a function which returns true if no two of those sets have any elements in common1 and false otherwise. Some of the test cases are a bit tricky, so pay a little more attention to them.

```
(defn pairwise
[xs]
(let [ls (for [x xs y xs :when (not= x y)] [x y])]
(apply = 0 (map #(count (clojure.set/intersection (first %) (second %))) ls))))
;; (pairwise #{#{'(:x :y :z) '(:x :y) '(:z) '()}
;; #{#{:x :y :z} #{:x :y} #{:z} #{}}
;; #{'[:x :y :z] [:x :y] [:z] [] {}}})
```

No. 100 Least Common Multiple Write a function which calculates the least common multiple. Your function should accept a variable number of positive integers or ratios.

```
(defn lcm
([x y & args]
(reduce lcm (conj args y x)))
([x y]
(let [gcd (fn [a b] (if (zero? b) a (recur b (rem a b))))]
(/ (* x y) (gcd x y)))))
;; (lcm 1/3 2/5)
```

### Medium

No. 54 Partition a Sequence Write a function which returns a sequence of lists of x items each. Lists of less than x items should not be returned.

```
(defn my-partition
([n x] (my-partition n x []))
([n x y]
(let [fpl (take n x)
spl (drop n x)]
(if (> n (count spl))
(conj y fpl)
(my-partition n spl (conj y fpl))))))
;; (my-partition 3 (range 8))
;; => [(0 1 2) (3 4 5)]
```

No. 74 Filter Perfect Squares Given a string of comma separated integers, write a function which returns a new comma separated string that only contains the numbers which are perfect squares.

```
(defn filter-sq
[s]
(let [xs (clojure.string/split s #",")
ms (map #(Integer/valueOf %) xs)]
(->> ms
(filter (fn [x]
(let [sqra (Math/sqrt x)]
(== sqra (int sqra)))))
(clojure.string/join #","))))
;; (filter-sq "4,5,6,7,8,9")
;; => "4,9"
```

## Takeaways

Some of the Easy problems weren’t all that “easy” to solve. I definitely benefited from working on them after a while. When I got started on them today, I was able to figure out solutions to them without much consternation.

Today’s tally -

- 3 Easy problems
- 2 Medium problems