aoc2024: day 1

2 files changed, 100 insertions, 0 deletions

diff --git a/aoc24/src/day1p1.zig b/aoc24/src/day1p1.zig
new file mode 100644
index 0000000..fba4b8c
--- /dev/null
+++ b/aoc24/src/day1p1.zig
@@ -0,0 +1,49 @@
+const std = @import("std");
+
+pub fn main() !void {
+    const input = @embedFile("1.txt");
+    try std.fmt.format(std.io.getStdOut().writer(), "{}\n", .{try run(input)});
+}
+
+test {
+    std.debug.assert(try run(
+        \\3   4
+        \\4   3
+        \\2   5
+        \\1   3
+        \\3   9
+        \\3   3
+    ) == 11);
+}
+
+pub fn run(input: []const u8) !u32 {
+    var lines = std.mem.split(u8, input, "\n");
+
+    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    defer arena.deinit();
+    const allocator = arena.allocator();
+
+    var lefts = std.ArrayList(u32).init(allocator);
+    defer lefts.deinit();
+    var rights = std.ArrayList(u32).init(allocator);
+    defer rights.deinit();
+
+    while (lines.next()) |line| {
+        if (line.len == 0) continue;
+        var words = std.mem.split(u8, line, "   ");
+        const left = try std.fmt.parseInt(u32, words.next() orelse return error.InvalidInput, 10);
+        const right = try std.fmt.parseInt(u32, words.next() orelse return error.InvalidInput, 10);
+        try lefts.append(left);
+        try rights.append(right);
+    }
+
+    std.mem.sort(u32, lefts.items, {}, std.sort.asc(u32));
+    std.mem.sort(u32, rights.items, {}, std.sort.asc(u32));
+
+    var sum: u32 = 0;
+    for (lefts.items, rights.items) |l, r| {
+        sum += @max(l, r) - @min(l, r);
+    }
+
+    return sum;
+}
diff --git a/aoc24/src/day1p2.zig b/aoc24/src/day1p2.zig
new file mode 100644
index 0000000..91b99fa
--- /dev/null
+++ b/aoc24/src/day1p2.zig
@@ -0,0 +1,51 @@
+const std = @import("std");
+
+pub fn main() !void {
+    const input = @embedFile("1.txt");
+    try std.fmt.format(std.io.getStdOut().writer(), "{}\n", .{try run(input)});
+}
+
+test {
+    std.debug.assert(try run(
+        \\3   4
+        \\4   3
+        \\2   5
+        \\1   3
+        \\3   9
+        \\3   3
+    ) == 31);
+}
+
+pub fn run(input: []const u8) !u32 {
+    var lines = std.mem.split(u8, input, "\n");
+
+    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    defer arena.deinit();
+    const allocator = arena.allocator();
+
+    var lefts = std.ArrayList(u32).init(allocator);
+    defer lefts.deinit();
+    var rights = std.AutoHashMap(u32, u16).init(allocator);
+    defer rights.deinit();
+
+    while (lines.next()) |line| {
+        if (line.len == 0) continue;
+        var words = std.mem.split(u8, line, "   ");
+        const left = try std.fmt.parseInt(u32, words.next() orelse return error.InvalidInput, 10);
+        const right = try std.fmt.parseInt(u32, words.next() orelse return error.InvalidInput, 10);
+        try lefts.append(left);
+        const entry = try rights.getOrPut(right);
+        if (entry.found_existing)
+            entry.value_ptr.* += 1
+        else
+            entry.value_ptr.* = 1;
+    }
+
+    var sum: u32 = 0;
+    for (lefts.items) |x| {
+        const count: u32 = @intCast(rights.get(x) orelse 0);
+        sum += x * count;
+    }
+
+    return sum;
+}