programming kata day 5

1 minute read

Code kata

Problem

Write a function to determine if a number is a triangular number.

Solutions

Solution 1

(defn nth-triangle [n]
  (apply + (range (inc n))))

(defn is-triangle-number [n]
  (loop [i 0]
    (cond (> n (nth-triangle i))
          (recur (inc i))
          (= n (nth-triangle i))
          true
          :else
          false)))

Solution 2

(defn is-triangle-number [n]
  (loop [tri 0
         i 1]
    (cond (> n tri)
          (recur (+ tri i) (inc i))
          (= n tri)
          true
          :else
          false)))

Note

Solution 1 is the first that came to my mind, but it has a typical problem: redundant calculation. Solution 2 solves it by keeping the last triangular number.

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