Advent of Awk 2019

I decided to solve this year’s Advent of Code problems using awk(1), a woefully underutilised unix tool and programming language. The below solutions may be run using the command:

awk -f solution.awk input.txt

Day 1

Puzzle 1

{ total += int($0 / 3.0) - 2 }
END { print total }

Puzzle 2

{ 
    fuel = int($0 / 3.0) - 2;
    while (fuel > 0) {
        total += fuel;
        fuel = int(fuel / 3.0) - 2;
    }
}
END { print total }

Day 2

These are a fair bit less elegant than the previous two solutions. I’m not entirely happy with the second, in particular the array copy, but it works.

Puzzle 1

BEGIN { RS = "," }
{ ops[i++] = $1  }
END {
    for (i = 0; ops[i] != 99; i += 4) {
        if (ops[i] == 1)
            ops[ops[i+3]] = ops[ops[i+1]] + ops[ops[i+2]];
        else if (ops[i] == 2)
            ops[ops[i+3]] = ops[ops[i+1]] * ops[ops[i+2]];
    }
    print ops[0];
}

Puzzle 2

BEGIN { RS = "," }
{ oops[i++] = $1  }
END {
    for (noun = 0; noun <= 99; noun++)
    for (verb = 0; verb <= 99; verb++) {
        for (op in oops) ops[op] = oops[op];
        ops[1] = noun;
        ops[2] = verb;
        for (i = 0; ops[i] != 99; i += 4) {
            if (ops[i] == 1)
                ops[ops[i+3]] = ops[ops[i+1]] + ops[ops[i+2]];
            else if (ops[i] == 2)
                ops[ops[i+3]] = ops[ops[i+1]] * ops[ops[i+2]];
        }
        if (ops[0] == 19690720) {
            print 100*noun + verb;
            exit 0;
        }
    }
}