p5_adding

#!/bin/sh
# https://blog.svpino.com/2015/05/07/five-programming-problems-every-software-engineer-should-be-able-to-solve-in-less-than-1-hour
# problem 5
# usage: ./p5_adding beg end goal
# e.g. : ./p5_adding 1 10 100
awk -v "beg=$1" -v "end=$2" -v "goal=$3" '
function f(cur, last, out, sum, op) {
    if (cur > end) {
        if (sum == goal)
            printf("%s\n", out)
        return
    }
    f(cur + 1, cur     , out " + " cur, sum + cur                        ,  1)
    f(cur + 1, cur     , out " - " cur, sum - cur                        , -1)
    f(cur + 1, last cur, out       cur, sum - op * last + op * (last cur), op)
}
BEGIN {
    f(beg + 1, beg, beg, beg, 1)
}'