# Rosalind: BA1M — Implement NumberToPattern
# https://rosalind.info/problems/ba1m/
#
# Given: Integers index and k.
# Return: NumberToPattern(index, k).

let index = 45
let k = 4

# The inverse of BA1L: read the index as a base-4 number, most significant digit
# first, with A=0, C=1, G=2, T=3.
let symbols = ["A", "C", "G", "T"]

let pattern = ""
let remaining = index
let position = 0
while position < k {
    let power = 1
    let e = 0
    while e < k - position - 1 {
        power = power * 4
        e = e + 1
    }
    let digit = int(remaining / power)
    pattern = pattern + symbols[digit]
    remaining = remaining - digit * power
    position = position + 1
}

println("Result:   " + pattern)
println("Expected: AGTC")

fn test_ba1m_number_to_pattern() {
    assert pattern == "AGTC", "BA1M: got " + pattern
    assert len(pattern) == k, "BA1M: wrong length"
}