advent-of-code-2023/day6/main.zig

const std = @import("std");

pub fn main() !void {
    // const times = [_]u8{ 7, 15, 30 };
    // const distances = [_]u8{ 9, 40, 200 };

    const times = [_]u8{ 50, 74, 86, 85 };
    const distances = [_]u16{ 242, 1017, 1691, 1252 };

    // Part 1
    var totals: u64 = 1;
    for (times, 0..) |time, idx| {
        var waysToWin: u8 = 0;
        for (0..time) |ms| {
            var dist: u16 = 0;
            for (0..time - ms) |_| {
                dist += @intCast(ms);
            }

            if (dist > distances[idx]) {
                waysToWin += 1;
            }
        }
        totals *= waysToWin;
    }

    std.debug.print("Part 1: {d}\n", .{totals});

    // Part 2
    // const time = 71530;
    // const distance = 940200;
    const time = 50748685;
    const distance = 242101716911252;

    var pivot: u32 = time / 2;
    var max: u32 = pivot;
    var min: u32 = 0;
    var prev: u32 = pivot;

    var i: u8 = 0;
    while (true) : (i += 1) {
        var dist: u64 = 0;
        for (0..(time - pivot)) |_| {
            dist += pivot;
        }

        if (dist > distance) {
            max = pivot;
            pivot -= (max - min) / 2;
        } else {
            min = pivot;
            pivot += (max - min) / 2;
        }

        if (prev == pivot) {
            break;
        }
        prev = pivot;
    }

    const num = time - (pivot * 2);
    std.debug.print("Part 2: {}\n", .{num});
    // TODO: potentially off by one. Could actually figure it out or just try num + 1 in AoC
}