I wrote the following code to produce a lazy sequence of the triangle
numbers. (triangle numbers are the series of numbers: 1, 1+2, 1+2+3,
etc...)
(defn tri-nums []
"prduce a lazy sequence of triangle numbers"
(let [triangles (map #(range 1 %) (iterate inc 2))]
(map #(reduce + %) triangles)))
However, I now have produced a large triangle number (76576500) and
want to know which triangle number it is (e.g. the first, second,
third, etc...)
So, I wrote the following code which should accept a triangle number
as input and tell you which one it is in the series:
(defn which-tri [z]
(loop [x 1 y (first (tri-nums))]
(cond
(= y z)
x
(< y z)
(recur (inc x) (first (rest (tri-nums))))
true
(println "no such tri-num"))))
The problem is that this function works for the first two triangle
numbers (1, 3), but then just sits there doing nothing on any higher
(6, 10, etc...).
Any thoughts?
thanks!
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