day 2 ;(

2024/02/p2/main.zig

@@ -0,0 +1,69 @@
+const std = @import("std");
+
+pub fn main() !void {
+    var file = try std.fs.cwd()
+        .openFile("../input.txt", .{});
+    defer file.close();
+
+    var buf_reader = std.io.bufferedReader(file.reader());
+    var in_stream = buf_reader.reader();
+
+    var buf: [64]u8 = undefined;
+    var t: u32 = 0;
+    out: while (try in_stream.readUntilDelimiterOrEof(&buf, '\n')) |line| {
+        var split_iter = std.mem.split(u8, line, " ");
+        const first_res = try check_list(&split_iter, null);
+        if (first_res != null) {
+            var res: ?usize = first_res;
+            var fail: usize = 0;
+            while (res != null) {
+                if (res.? < fail) {
+                    // std.debug.print(".. {s}\n", .{line});
+                    continue :out;
+                }
+                var split_iter_l = std.mem.split(u8, line, " ");
+                res = try check_list(&split_iter_l, fail);
+                fail += 1;
+            }
+        }
+
+        t += 1;
+    }
+    std.debug.print("Total {d}\n", .{t});
+}
+
+pub fn sameSign(n1: i8, n2: i8) bool {
+    return (n1 < 0) == (n2 < 0);
+}
+
+// null if everythin alr
+// idx num of failure otherwise
+pub fn check_list(iter: *std.mem.SplitIterator(u8, .sequence), skip: ?usize) !?usize {
+    var dir: i8 = 0;
+    var i: usize = 0;
+    if (skip != null and skip.? == 0) {
+        _ = iter.next();
+        i = 1;
+    }
+    var prev = try std.fmt.parseInt(i8, iter.next().?, 10);
+    while (iter.next()) |strnum| {
+        i += 1;
+        if (skip != null and skip.? == i) {
+            continue;
+        }
+        const n = try std.fmt.parseInt(i8, strnum, 10);
+        // std.debug.print("i={d} prev={} sk={any} n={}\n", .{ i, prev, skip, n });
+        const d = prev - n;
+        if (d == 0 or @abs(d) > 3) {
+            return i;
+        }
+
+        if (dir == 0) {
+            dir = d;
+        } else if (!sameSign(dir, d)) {
+            return i;
+        }
+        prev = n;
+    }
+    return null;
+}