day 1

day1/day1_part2.zig

@@ -0,0 +1,60 @@
+const std = @import("std");
+
+pub fn main() !void {
+    const file = try std.fs.cwd().openFile("input2", .{});
+    const file_reader = file.reader();
+    defer file.close();
+
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    const ally = gpa.allocator();
+    defer _ = gpa.deinit();
+
+    var left = std.ArrayList(u32).init(ally);
+    var right = std.ArrayList(u32).init(ally);
+    defer left.deinit();
+    defer right.deinit();
+
+    var input_buf = std.ArrayListUnmanaged(u8){};
+    defer input_buf.deinit(ally);
+    while (true) {
+        defer input_buf.clearRetainingCapacity();
+        file_reader.streamUntilDelimiter(input_buf.writer(ally), '\n', null) catch |err| switch (err) {
+            error.EndOfStream => break,
+            else => return err,
+        };
+
+        var integers = std.mem.splitSequence(u8, input_buf.items, "   ");
+
+        const first = std.fmt.parseInt(u32, integers.next().?, 10) catch |err| {
+            std.debug.print("Error parsing first integer: {}\n", .{err});
+            continue;
+        };
+        const second = std.fmt.parseInt(u32, integers.next().?, 10) catch |err| {
+            std.debug.print("Error parsing second integer: {}\n", .{err});
+            continue;
+        };
+
+        try left.append(first);
+        try right.append(second);
+
+        // std.debug.print("Integers are '{}' and '{}' of types {} and {}\n", .{ first, second, @TypeOf(first), @TypeOf(second) });
+    }
+
+    std.mem.sort(u32, left.items, {}, comptime std.sort.asc(u32));
+    std.mem.sort(u32, right.items, {}, comptime std.sort.asc(u32));
+
+    // We have the two sorted arrays. Now, similarity score
+    var occurances = std.AutoHashMap(u32, usize).init(ally);
+    defer occurances.deinit();
+    for (left.items) |element| {
+        const needle = &[_]u32{element};
+        _ = try occurances.put(element, std.mem.count(u32, right.items, needle));
+    }
+
+    var n_occurances: u64 = 0;
+    for (left.items) |element| {
+        n_occurances += element * occurances.get(element).?;
+    }
+
+    std.debug.print("{}\n", .{ n_occurances });
+}