70 lines
2.1 KiB
C#
70 lines
2.1 KiB
C#
namespace AOC2020;
|
|
|
|
/// <summary>
|
|
/// Day 18: <see href="https://adventofcode.com/2020/day/18" />
|
|
/// </summary>
|
|
public sealed class Day18 : Day
|
|
{
|
|
private readonly List<string> _expressions;
|
|
|
|
public Day18() : base(2020, 18, "Operation Order") =>
|
|
_expressions = Input.Select(line => line.Replace(" ", "")).ToList();
|
|
|
|
private static long Calculate(string expr, Func<char, int> precedence)
|
|
{
|
|
var postfixNotation = new StringBuilder();
|
|
var postfixStack = new Stack<char>();
|
|
|
|
foreach (var c in expr)
|
|
if (char.IsDigit(c))
|
|
{
|
|
postfixNotation.Append(c);
|
|
}
|
|
else if (c == '(')
|
|
{
|
|
postfixStack.Push(c);
|
|
}
|
|
else if (c == ')')
|
|
{
|
|
while (postfixStack.Count > 0 && postfixStack.Peek() != '(')
|
|
postfixNotation.Append(postfixStack.Pop());
|
|
|
|
postfixStack.TryPop(out _);
|
|
}
|
|
else
|
|
{
|
|
while (postfixStack.Count > 0 && precedence(c) <= precedence(postfixStack.Peek()))
|
|
postfixNotation.Append(postfixStack.Pop());
|
|
|
|
postfixStack.Push(c);
|
|
}
|
|
|
|
while (postfixStack.Count > 0)
|
|
postfixNotation.Append(postfixStack.Pop());
|
|
|
|
var expressionStack = new Stack<long>();
|
|
|
|
foreach (var c in postfixNotation.ToString())
|
|
if (char.IsDigit(c))
|
|
{
|
|
expressionStack.Push((long)char.GetNumericValue(c));
|
|
}
|
|
else
|
|
{
|
|
var a = expressionStack.Pop();
|
|
var b = expressionStack.Pop();
|
|
|
|
if (c == '+') expressionStack.Push(a + b);
|
|
if (c == '*') expressionStack.Push(a * b);
|
|
}
|
|
|
|
return expressionStack.Pop();
|
|
}
|
|
|
|
public override string Part1() =>
|
|
$"{_expressions.Sum(expr => Calculate(expr, c => c == '+' || c == '*' ? 1 : 0))}";
|
|
|
|
public override string Part2() =>
|
|
$"{_expressions.Sum(expr => Calculate(expr, c => c switch { '+' => 2, '*' => 1, _ => 0 }))}";
|
|
}
|