day 2 ;(

2024/02/p2/test.zig

@@ -0,0 +1,44 @@
+const std = @import("std");
+
+pub fn main() !void {
+    const line = "50 29 30 31 34 35 37";
+    var iter = std.mem.split(u8, line, " ");
+    const res = check_list(&iter, 0);
+    std.debug.print("{any}\n", .{res});
+}
+
+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;
+}