Solve day 4

src/day04.zig

@@ -0,0 +1,55 @@
+const std = @import("std");
+
+pub const input = @embedFile("input/day04.txt");
+const test_input = @embedFile("input/day04_test1.txt");
+
+const Range = struct {
+    start: usize,
+    end: usize,
+    fn parse(str: []const u8) !Range {
+        var range_parts = std.mem.tokenize(u8, str, "-");
+        const range = Range{
+            .start = try std.fmt.parseInt(usize, range_parts.next().?, 10),
+            .end = try std.fmt.parseInt(usize, range_parts.next().?, 10),
+        };
+        return range;
+    }
+    fn contains(self: Range, other: Range) bool {
+        return (other.start >= self.start and other.end <= self.end);
+    }
+    fn overlaps(self: Range, other: Range) bool {
+        return (self.start <= other.end and self.end >= other.start);
+    }
+};
+
+pub fn solve_part1(data: []const u8) !usize {
+    var lines = std.mem.tokenize(u8, data, "\n");
+    var count: usize = 0;
+    while (lines.next()) |line| {
+        var elves = std.mem.tokenize(u8, line, ",");
+        const range1 = try Range.parse(elves.next().?);
+        const range2 = try Range.parse(elves.next().?);
+        if (range1.contains(range2) or range2.contains(range1)) count += 1;
+    }
+    return count;
+}
+
+pub fn solve_part2(data: []const u8) !usize {
+    var lines = std.mem.tokenize(u8, data, "\n");
+    var count: usize = 0;
+    while (lines.next()) |line| {
+        var elves = std.mem.tokenize(u8, line, ",");
+        const range1 = try Range.parse(elves.next().?);
+        const range2 = try Range.parse(elves.next().?);
+        if (range1.overlaps(range2)) count += 1;
+    }
+    return count;
+}
+
+test "solves part1" {
+    try std.testing.expectEqual(solve_part1(test_input), 2);
+}
+
+test "solves part2" {
+    try std.testing.expectEqual(solve_part2(test_input), 4);
+}

src/input/day04_test1.txt

@@ -0,0 +1,6 @@
+2-4,6-8
+2-3,4-5
+5-7,7-9
+2-8,3-7
+6-6,4-6
+2-6,4-8

src/main.zig

@@ -3,6 +3,7 @@ const std = @import("std");
 const day01 = @import("day01.zig");
 const day02 = @import("day02.zig");
 const day03 = @import("day03.zig");
+const day04 = @import("day04.zig");
 const utils = @import("utils.zig");
 
 fn solve_day(comptime day_num: u8, day: anytype, stdout: anytype, timer: *std.time.Timer) !void {
@@ -30,6 +31,7 @@ pub fn main() !void {
     try solve_day(1, day01, &stdout, &timer);
     try solve_day(2, day02, &stdout, &timer);
     try solve_day(3, day03, &stdout, &timer);
+    try solve_day(4, day04, &stdout, &timer);
 
     try bw.flush();
 }
@@ -40,5 +42,6 @@ test {
     _ = day01;
     _ = day02;
     _ = day03;
+    _ = day04;
     _ = utils;
 }