day 5 part 1

day4.zig

@@ -0,0 +1,236 @@
+const std = @import("std");
+
+const utils = @import("utils.zig");
+
+pub fn main() !void {
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    const alloc = gpa.allocator();
+
+    const filename = "inputs/day4.txt";
+
+    {
+        const file_reader = try utils.FileReader.init(alloc, filename);
+        defer file_reader.deinit();
+
+        const result = try part1(alloc, file_reader.reader());
+
+        try std.io.getStdOut().writer().print("Day 4, part 1: {}\n", .{result});
+    }
+
+    {
+        const file_reader = try utils.FileReader.init(alloc, filename);
+        defer file_reader.deinit();
+
+        const result = try part2(alloc, file_reader.reader());
+
+        try std.io.getStdOut().writer().print("Day 4, part 2: {}\n", .{result});
+    }
+}
+
+fn check(grid: []const []const u8, needle: []const u8, i: usize, j: usize, i_step: usize, j_step: usize) bool {
+    var idx = i;
+    var jdx = j;
+
+    for (0..needle.len) |n| {
+        if (grid[idx][jdx] != needle[n]) {
+            return false;
+        }
+
+        idx +%= i_step;
+        jdx +%= j_step;
+    }
+
+    return true;
+}
+
+fn part1(alloc: std.mem.Allocator, reader: anytype) !u32 {
+    const input = try reader.readAllAlloc(alloc, std.math.maxInt(usize));
+    defer alloc.free(input);
+
+    // number of lines in number of newline + 1
+    // except if the last line is empty, then one less
+    var num_lines = std.mem.count(u8, input, "\n") + 1;
+    if (input[input.len - 1] == '\n') {
+        num_lines -= 1;
+    }
+
+    const grid = try alloc.alloc([]const u8, num_lines);
+    defer alloc.free(grid);
+
+    // var it = std.mem.splitScalar(u8, input, '\n');
+    var it = std.mem.tokenizeScalar(u8, input, '\n');
+
+    const line_length = it.peek().?.len;
+
+    for (grid) |*grid_line| {
+        const line = it.next().?;
+
+        std.debug.assert(line.len == line_length);
+
+        grid_line.* = line;
+    }
+
+    std.debug.assert(it.next() == null);
+
+    const xmas = "XMAS";
+    const samx = "SAMX";
+
+    var count: u32 = 0;
+
+    for (0..num_lines) |i| {
+        for (0..line_length - 3) |j| {
+            if (check(grid, xmas, i, j, 0, 1)) {
+                count += 1;
+            } else if (check(grid, samx, i, j, 0, 1)) {
+                count += 1;
+            }
+        }
+    }
+
+    for (0..line_length) |j| {
+        for (0..num_lines - 3) |i| {
+            if (check(grid, xmas, i, j, 1, 0)) {
+                count += 1;
+            } else if (check(grid, samx, i, j, 1, 0)) {
+                count += 1;
+            }
+        }
+    }
+
+    for (0..num_lines - 3) |i| {
+        for (0..line_length - 3) |j| {
+            if (check(grid, xmas, i, j, 1, 1)) {
+                count += 1;
+            } else if (check(grid, samx, i, j, 1, 1)) {
+                count += 1;
+            }
+
+            if (check(grid, xmas, i, j + 3, 1, std.math.maxInt(usize))) {
+                count += 1;
+            } else if (check(grid, samx, i, j + 3, 1, std.math.maxInt(usize))) {
+                count += 1;
+            }
+        }
+    }
+
+    return count;
+}
+
+fn part2(alloc: std.mem.Allocator, reader: anytype) !u32 {
+    const input = try reader.readAllAlloc(alloc, std.math.maxInt(usize));
+    defer alloc.free(input);
+
+    // number of lines in number of newline + 1
+    // except if the last line is empty, then one less
+    var num_lines = std.mem.count(u8, input, "\n") + 1;
+    if (input[input.len - 1] == '\n') {
+        num_lines -= 1;
+    }
+
+    const grid = try alloc.alloc([]const u8, num_lines);
+    defer alloc.free(grid);
+
+    // var it = std.mem.splitScalar(u8, input, '\n');
+    var it = std.mem.tokenizeScalar(u8, input, '\n');
+
+    const line_length = it.peek().?.len;
+
+    for (grid) |*grid_line| {
+        const line = it.next().?;
+
+        std.debug.assert(line.len == line_length);
+
+        grid_line.* = line;
+    }
+
+    std.debug.assert(it.next() == null);
+
+    const mas = "MAS";
+    const sam = "SAM";
+
+    var count: u32 = 0;
+
+    for (0..num_lines - 2) |i| {
+        for (0..line_length - 2) |j| {
+            if (check(grid, sam, i, j, 1, 1) or check(grid, mas, i, j, 1, 1)) {
+                if (check(grid, sam, i, j + 2, 1, std.math.maxInt(usize)) or check(grid, mas, i, j + 2, 1, std.math.maxInt(usize))) {
+                    count += 1;
+                }
+            }
+        }
+    }
+
+    return count;
+}
+
+test "part1 example" {
+    const alloc = std.testing.allocator;
+
+    const example =
+        \\MMMSXXMASM
+        \\MSAMXMSMSA
+        \\AMXSXMAAMM
+        \\MSAMASMSMX
+        \\XMASAMXAMM
+        \\XXAMMXXAMA
+        \\SMSMSASXSS
+        \\SAXAMASAAA
+        \\MAMMMXMMMM
+        \\MXMXAXMASX
+    ;
+
+    var stream = std.io.fixedBufferStream(example);
+
+    const result = try part1(alloc, stream.reader());
+
+    try std.testing.expect(result == 18);
+}
+
+test "part1 input" {
+    const alloc = std.testing.allocator;
+
+    const filename = "inputs/day4.txt";
+
+    const file_reader = try utils.FileReader.init(alloc, filename);
+    defer file_reader.deinit();
+
+    const result = try part1(alloc, file_reader.reader());
+
+    try std.testing.expect(result == 2593);
+}
+
+test "part2 example" {
+    const alloc = std.testing.allocator;
+
+    const example =
+        \\MMMSXXMASM
+        \\MSAMXMSMSA
+        \\AMXSXMAAMM
+        \\MSAMASMSMX
+        \\XMASAMXAMM
+        \\XXAMMXXAMA
+        \\SMSMSASXSS
+        \\SAXAMASAAA
+        \\MAMMMXMMMM
+        \\MXMXAXMASX
+    ;
+
+    var stream = std.io.fixedBufferStream(example);
+
+    const result = try part2(alloc, stream.reader());
+
+    try std.testing.expect(result == 9);
+}
+
+test "part2 input" {
+    const alloc = std.testing.allocator;
+
+    const filename = "inputs/day4.txt";
+
+    const file_reader = try utils.FileReader.init(alloc, filename);
+    defer file_reader.deinit();
+
+    const result = try part2(alloc, file_reader.reader());
+
+    try std.testing.expect(result == 1950);
+}