day 2

src/days/day2.zig

@@ -0,0 +1,74 @@
+const std = @import("std");
+
+pub fn day2pt1(ranges: []const u8) !usize {
+    var i = std.mem.splitScalar(u8, ranges, ',');
+    var sum: usize = 0;
+    while (i.next()) |range| {
+        var j = std.mem.splitScalar(u8, range, '-');
+        const range_start = try std.fmt.parseInt(usize, j.next().?, 10);
+        const range_end = try std.fmt.parseInt(usize, j.next().?, 10);
+
+        var k = range_start;
+        const max_len = 32;
+        var buf: [max_len]u8 = undefined;
+        while (k <= range_end) {
+            const current_id = try std.fmt.bufPrint(&buf, "{d}", .{k});
+            if (current_id.len % 2 == 0) {
+                const half = current_id.len / 2;
+                if (std.mem.eql(u8, current_id[0..half], current_id[half..current_id.len])) {
+                    sum += k;
+                }
+            }
+            k += 1;
+        }
+    }
+    return sum;
+}
+
+pub fn day2pt2(ranges: []const u8) !usize {
+    var i = std.mem.splitScalar(u8, ranges, ',');
+    var sum: usize = 0;
+    while (i.next()) |range| {
+        var j = std.mem.splitScalar(u8, range, '-');
+        const range_start = try std.fmt.parseInt(usize, j.next().?, 10);
+        const range_end = try std.fmt.parseInt(usize, j.next().?, 10);
+
+        var k = range_start;
+        const max_len = 32;
+        var buf: [max_len]u8 = undefined;
+        while (k <= range_end) {
+            const current_id = try std.fmt.bufPrint(&buf, "{d}", .{k});
+            const len = current_id.len;
+            var found = false;
+            // Try all possible substring lengths that divide the length - should be made more efficient （＞人＜；）
+            for (1..len / 2 + 1) |sub_len| {
+                if (len % sub_len != 0) continue;
+                const repeats = len / sub_len;
+                if (repeats < 2) continue;
+                const sub = current_id[0..sub_len];
+                var valid = true;
+                for (1..repeats) |r| {
+                    if (!std.mem.eql(u8, sub, current_id[r * sub_len .. (r + 1) * sub_len])) {
+                        valid = false;
+                        break;
+                    }
+                }
+                if (valid) {
+                    found = true;
+                    break;
+                }
+            }
+            if (found) {
+                sum += k;
+            }
+            k += 1;
+        }
+    }
+    return sum;
+}
+
+test "Day 2 example testing" {
+    const example_input = "11-22,95-115,998-1012,1188511880-1188511890,222220-222224,1698522-1698528,446443-446449,38593856-38593862,565653-565659,824824821-824824827,2121212118-2121212124";
+    try std.testing.expectEqual(try day2pt1(example_input), 1227775554);
+    try std.testing.expectEqual(try day2pt2(example_input), 4174379265);
+}