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113 lines
3.7 KiB
Zig
113 lines
3.7 KiB
Zig
const std = @import("std");
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const lib = @import("lib.zig");
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const Number = struct { row: usize, col: usize, length: usize, value: u32 };
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pub fn main() !void {
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const content = @embedFile("data.txt");
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const grid = try lib.splitArrayIntoArrayList(content, "\n");
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defer grid.deinit();
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const numbers = try parseNumbers(grid);
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defer numbers.deinit();
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var total1: u128 = 0;
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for (numbers.items) |n| {
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if (numberTouchesSymbol(n, grid)) {
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total1 += n.value;
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}
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}
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std.debug.print("total1 {d}\n", .{total1});
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var total2: u128 = 0;
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for (grid.items, 0..) |line, row| {
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for (line, 0..) |val, col| {
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if (val == '*') {
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total2 += try findGearRatio(row, col, numbers);
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}
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}
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}
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std.debug.print("total2 {d}\n", .{total2});
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}
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fn findGearRatio(row: usize, col: usize, numbers: std.ArrayList(Number)) !u32 {
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const touching = try findNumbersTouchingCell(row, col, numbers);
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if (touching.items.len != 2) {
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return 0;
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}
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return touching.items[0].value * touching.items[1].value;
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}
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fn findNumbersTouchingCell(row: usize, col: usize, numbers: std.ArrayList(Number)) !std.ArrayList(Number) {
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const allocator = std.heap.page_allocator;
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var touching = std.ArrayList(Number).init(allocator);
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for (numbers.items) |n| {
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// itreate over each digit in the number
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for (0..n.length) |i| {
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// TODO: upgrade to Zig .12 to get @abs
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// if (@abs(n.row - row) < 1 and @abs(n.col + i - col) < 1) {
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if ((n.row == row or n.row + 1 == row or n.row == row + 1) and (n.col + i == col or n.col + 1 + i == col or n.col + i == col + 1)) {
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try touching.append(n);
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break;
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}
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}
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}
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return touching;
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}
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fn numberTouchesSymbol(n: Number, grid: std.ArrayList([]const u8)) bool {
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const items = grid.items;
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const width = items[0].len;
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const height = items.len - 1; // TODO: fix extra crap when i read files..
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// itreate over each digit in the number
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for (0..n.length) |i| {
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// over the 3 nearest rows
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for (0..3) |r| {
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// and the 3 nearest columns
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for (0..3) |c| {
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const outOfBounds = (r == 0 and n.row == 0) or (c == 0 and n.col + i == 0) or (r == 2 and n.row + 1 == height) or (c == 2 and n.col + i + 1 == width);
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if (!outOfBounds) {
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const row = n.row + r - 1;
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const col = n.col + c + i - 1;
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const val = items[row][col];
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if (!std.ascii.isDigit(val) and val != '.') {
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return true;
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}
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}
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}
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}
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}
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return false;
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}
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fn parseNumbers(grid: std.ArrayList([]const u8)) !std.ArrayList(Number) {
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const allocator = std.heap.page_allocator;
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var numbers = std.ArrayList(Number).init(allocator);
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for (grid.items, 0..) |line, row| {
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var numList = std.ArrayList(u8).init(allocator);
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defer numList.deinit();
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for (line, 0..) |val, col| {
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if (std.ascii.isDigit(val)) {
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try numList.append(val);
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}
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// if we have a number started, and we've encountered a non-digit (or the end of the grid)
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if (numList.items.len != 0 and (!std.ascii.isDigit(val) or col == line.len - 1)) {
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const parsed = try std.fmt.parseInt(u32, numList.items, 10);
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const length = numList.items.len;
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try numbers.append(Number{ .row = row, .col = col - length, .length = length, .value = parsed });
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numList.items.len = 0;
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}
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}
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}
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return numbers;
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}
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