As you enter this room, you hear a loud click! Some of the tiles in the floor here seem to be pressure plates for traps, and the trap you just triggered has run out of... whatever it tried to do to you. You doubt you'll be so lucky next time.

Upon closer examination, the traps and safe tiles in this room seem to follow a pattern. The tiles are arranged into rows that are all the same width; you take note of the safe tiles (.) and traps (^) in the first row (your puzzle input).

Read the full puzzle.

using System.Linq;
using System.Text;

namespace AdventOfCode.Y2016.Day18;

[ProblemName("Like a Rogue")]
class Solution : Solver {

    public object PartOne(string input) => SafeCount(input, 40);

    public object PartTwo(string input) => SafeCount(input, 400000);

    int SafeCount(string input, int lines) {
        var rowPrev = input;
        var safeCount = rowPrev.Count(ch => ch == '.');
        for (int i = 0; i < lines - 1; i++) {
            StringBuilder sb = new StringBuilder();
            for (int j = 0; j < rowPrev.Length; j++) {
                var leftTrap = j != 0 && rowPrev[j - 1] == '^';
                var centerTrap = rowPrev[j] == '^';
                var rightTrap = j != rowPrev.Length - 1 && rowPrev[j + 1] == '^';

                var trap =
                    (leftTrap && centerTrap && !rightTrap) ||
                    (!leftTrap && centerTrap && rightTrap) ||
                    (leftTrap && !centerTrap && !rightTrap) ||
                    (!leftTrap && !centerTrap && rightTrap)
                    ;
                sb.Append(trap ? '^' : '.');
            }
            rowPrev = sb.ToString();
            safeCount += rowPrev.Count(ch => ch == '.');
        }

        return safeCount;
    }
}

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