2024 Day 2 Part 1

2024/src/day02.zig

@@ -0,0 +1,97 @@
+const std = @import("std");
+const aoc = @import("aoc.zig");
+
+pub fn main() !void {
+    var gpa: std.heap.GeneralPurposeAllocator(.{}) = .{};
+    defer _ = gpa.deinit();
+    const allocator = gpa.allocator();
+
+    const file = try std.fs.cwd().openFile("input/day02.txt", .{});
+    defer file.close();
+
+    const stdout_file = std.io.getStdOut().writer();
+    var bw = std.io.bufferedWriter(stdout_file);
+    const stdout = bw.writer();
+
+    var lines = aoc.Lines.init(allocator, file);
+    defer lines.deinit();
+
+    var reports = std.ArrayList(Report).init(allocator);
+    defer reports.deinit();
+
+    while (try lines.next()) |line| {
+        const report = try Report.parse(allocator, line);
+        try reports.append(report);
+    }
+
+    try stdout.print("{d}\n", .{part1(reports)});
+    try bw.flush();
+
+    for (reports.items) |r| {
+        r.deinit();
+    }
+}
+
+const Report = struct {
+    levels: std.ArrayList(u32),
+
+    fn parse(allocator: std.mem.Allocator, line: std.ArrayList(u8)) !Report {
+        var levels = std.ArrayList(u32).init(allocator);
+
+        var it = std.mem.tokenizeScalar(u8, line.items, ' ');
+        while (it.next()) |level| {
+            const i = try std.fmt.parseInt(u32, level, 10);
+            try levels.append(i);
+        }
+
+        return .{ .levels = levels };
+    }
+
+    fn deinit(self: Report) void {
+        self.levels.deinit();
+    }
+
+    fn is_safe(self: Report) bool {
+        var prev = self.levels.items[0];
+
+        const sign = self.levels.items[1] > self.levels.items[0];
+
+        var i: usize = 1;
+        while (i < self.levels.items.len) {
+            const next = self.levels.items[i];
+            const diff = abs_diff(next, prev);
+
+            if ((next > prev) != sign) {
+                return false;
+            }
+
+            if (diff < 1 or diff > 3) {
+                return false;
+            }
+
+            prev = next;
+            i += 1;
+        }
+
+        return true;
+    }
+};
+
+fn abs_diff(a: u32, b: u32) u32 {
+    if (a > b) {
+        return a - b;
+    } else {
+        return b - a;
+    }
+}
+
+fn part1(reports: std.ArrayList(Report)) u32 {
+    var n: u32 = 0;
+    for (reports.items) |report| {
+        if (report.is_safe()) {
+            n += 1;
+        }
+    }
+
+    return n;
+}