##-
# Author: Brian Tiffin
# Dedicated to the public domain
#
# Date: October 2016
# Modified: 2016-10-17/05:47-0400
##+
#
# twosum.icn, find two array elements that add up to a given sum
# a modification of http://rosettacode.org/wiki/Two_Sum
#
link fullimag
procedure main(arglist)
    # predictable results for the UP docset
    &random := 1

    # target sum
    sum := pop(arglist) | ?100

    # create a list of the rest of the arguments, or make it up
    L := []
    if *arglist > 0 then every put(L, integer(!arglist))
    else every 1 to 20 do put(L, ?100)
    writes(sum, ", ")
    write(fullimage(L))

    # keep track of result count
    results := 0
    every write(fullimage(pair := twosum(sum, L)), " ",
        L[pair[1]], " ", L[pair[2]]) do results +:= 1
    if results = 0 then write("[], no solution")
end

# O(n^2), nested iterations
procedure twosum(sum, L)
    every i := 1 to *L-1 do
        every j := i+1 to *L do
            if L[i] + L[j] = sum then suspend [i,j]
end