Triangle number check

A triangle number is a number where n objects form an equilateral triangle (it's a bit hard to explain). For example, 6 is a triangle number because you can arrange 6 objects into an equilateral triangle:

寫一個可以確認數字是否為 triangle number 的函式

;; 6 is a triangle number

  1
 2 3
4 5 6

;; 8 is not a triangle number

   1
  2 3
 4 5 6
7 8

Solution

(ns nb-triangle.core)

(defn is-triangle-number [n]
  (loop [iter 1
         acc  0]
  (if (>= acc n)
    (= acc n)
    (recur (inc iter) (+ acc iter))))
)