Cfrtjryk

I decided to do Advent of Code this year in D, and the following is my solution to day8.

Algorithm aside, I was specifically wondering if there was a better way to use ranges in a recursive manner here. I feel like I should be able to do write the functions in a more generic way (not just int, avoiding the .array in main), and without destroying the original array in the process - avoiding the temporary variable p1.

My use of the header variable seems suspect to me as well - basically I want a popFront that returns a value, I think, but have been unable to find anything like that

I'm also happy to hear general advice about usual best practices and efficiencies

import std.algorithm;

import std.conv;

import std.file;

import std.range;

import std.stdio;

import std.string;



int count_metadata(ref int r)

{

    auto header = r.take(2);

    int num_child = header.front;

    int num_metadata = header.back;

    r = r.drop(2);

    int count;

    for (int i; i < num_child; i++) {

        count += r.count_metadata;

    }

    count += r.take(num_metadata).sum;

    r = r.drop(num_metadata);

    return count;

}



int node_value(ref int r)

{

    auto header = r.take(2);

    int num_child = header.front;

    int num_metadata = header.back;

    r = r.drop(2);

    int child_values;

    for (int i; i < num_child; i++) {

        child_values ~= node_value(r);

    }

    int count;

    if (num_child == 0) {

        count = r.take(num_metadata).sum;

    } else {

        // ignore out of range

        count = r.take(num_metadata).filter!(a => 0 < a && a <= child_values.length).map!(a => child_values[a - 1]).sum;

    }

    r = r.drop(num_metadata);

    return count;

}



void main(string args)

{

    // integers separated by spaces

    auto input = readText(args[1]).split.map!(a => to!int(a)).array;

    //auto input = [2, 3, 0, 3, 10, 11, 12, 1, 1, 0, 1, 99, 2, 1, 1, 2];

    auto p1 = input.dup;

    writeln("Metadata total: ", count_metadata(p1));

    writeln("Node value: ", node_value(input));

}

(args[1] is a file with integers separated by spaces, sample input is commented out below it)