day 4

2

@@ -0,0 +1,78 @@
+const std = @import("std");
+const input = @embedFile("test");
+
+fn string_from_grid_intervals(grid: [][]const u8, y1: u64, y2: u64, x1: u64, x2: u64, ally: std.mem.Allocator) ![]const u8 {
+    var result = std.ArrayList(u8).init(ally);
+    defer result.deinit();
+    std.debug.print("y1: {d} y2: {d} x1: {d} x2: {d}\n", .{ y1, y2, x1, x2 });
+    for (grid[y1..y2]) |row| {
+        for (row[x1..x2]) |c| {
+            std.debug.print("{c}", .{ c });
+            try result.append(c);
+        }
+    }
+    return result.toOwnedSlice();
+}
+
+fn xmas_exists(grid: [][]const u8, x: u64, y: u64, x_len: u64, y_len: u64, ally: std.mem.Allocator) bool {
+    var exists = false;
+
+    // Right
+    if (x_len >= x + 4) {
+        exists = exists or std.mem.eql(u8, grid[y][x..x+4], "XMAS");
+    }
+    // Left
+    if (!exists and x >= 3) {
+        exists = exists or std.mem.eql(u8, grid[y][x-3..x+1], "XMAS");
+    }
+    // Top
+    if (!exists and y >= 3) {
+        exists = exists or std.mem.eql(u8, string_from_grid_intervals(grid, y-3, y+1, x, x+1, ally), "XMAS");
+    }
+    // Bottom
+    if (!exists and y_len >= y + 4) {
+        exists = exists or std.mem.eql(u8, string_from_grid_intervals(grid, y, y+4, x, x+1, ally), "XMAS");
+    }
+
+    // Top Right
+    if (!exists and x_len >= x + 4 and y - 3 >= 0) {
+        exists = exists or std.mem.eql(u8, string_from_grid_intervals(grid, y-3, y+1, x, x+4, ally), "XMAS");
+    }
+    // Bottom Right
+    if (!exists and x_len >= x + 4 and y_len >= y + 4) {
+        exists = exists or std.mem.eql(u8, string_from_grid_intervals(grid, y, y+4, x, x+4, ally), "XMAS");
+    }
+    // Top Left
+    if (!exists and x - 3 >= 0 and y - 3 >= 0) {
+        exists = exists or std.mem.eql(u8, string_from_grid_intervals(grid, y-3, y+1, x-3, x+1, ally), "XMAS");
+    }
+    // Bottom Left
+    if (!exists and x - 3 >= 0 and y_len >= y + 4) {
+        exists = exists or std.mem.eql(u8, string_from_grid_intervals(grid, y, y+4, x-3, x+1, ally), "XMAS");
+    }
+    return exists;
+}
+
+pub fn main() !void {
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    const ally = gpa.allocator();
+    defer _ = gpa.deinit();
+
+    var lines = std.mem.tokenize(u8, input, "\r\n");
+
+    var grid = std.ArrayList([]const u8).init(ally);
+    defer grid.deinit();
+
+    while (lines.next()) |line| {
+        if (line.len > 0) {
+            try grid.append(line);
+        }
+    }
+
+    var xmas: u16 = 0;
+    for (grid.items, 0..) |row, y| {
+        for (row, 0..) |_, x| {
+            if (xmas_exists(grid.items, x, y, row.len, grid.items.len, ally)) xmas += 1;
+        }
+    }
+}