As the expedition finally reaches the extraction point, several large hot air balloons drift down to meet you. Crews quickly start unloading the equipment the balloons brought: many hot air balloon kits, some fuel tanks, and a fuel heating machine.

The fuel heating machine is a new addition to the process. When this mountain was a volcano, the ambient temperature was more reasonable; now, it's so cold that the fuel won't work at all without being warmed up first.

Read the full puzzle.

using System.Linq;
using System;

namespace AdventOfCode.Y2022.Day25;

[ProblemName("Full of Hot Air")]
class Solution : Solver {

    public object PartOne(string input) =>
        LongToSnafu(
            input
                .Split("\n")
                .Select(SnafuToLong)
                .Sum()
        );
    
    // This is just string to number conversion in base 5
    // with the two special digits that's worth -2 and -1.
    long SnafuToLong(string snafu) {
        long res = 0L;
        foreach (var digit in snafu) {
            res = res * 5;
            switch (digit) {
                case '=': res += -2; break;
                case '-': res += -1; break;
                case '0': res += 0; break;
                case '1': res += 1; break;
                case '2': res += 2; break;
            }
        }
        return res;
    }

    // Snafu numbers have digits -2, -1, 0, 1 and 2, so this is almost 
    // standard base 5 conversion, but when dealing with digits 3 and 4 we 
    // need to increment the higher decimal place so that we have
    // something to subtract 2 and 1 from.
    string LongToSnafu(long d) {
        var res = "";
        while (d > 0) {
            switch (d % 5) {
                case 0: res = '0' + res; break;
                case 1: res = '1' + res; break;
                case 2: res = '2' + res; break;
                // add 5 and emit -2 because 3 = 5 -2
                case 3: d+=5; res = '=' + res; break; 
                // add 5 and emit -1 because 4 = 5 -1
                case 4: d+=5; res = '-' + res; break;
            }
            d /= 5;
        }
        return res;
    }
}

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