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const std = @import("std");
pub fn main() !void {
const input = @embedFile("2.txt");
try std.fmt.format(std.io.getStdOut().writer(), "{}\n", .{try run(input)});
}
test {
const value = try run(
\\7 6 4 2 1
\\1 2 7 8 9
\\9 7 6 2 1
\\1 3 2 4 5
\\8 6 4 4 1
\\1 3 6 7 9
);
std.debug.print("got {}\n", .{value});
std.debug.assert(value == 4);
}
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 reports = std.ArrayList(std.ArrayList(u32)).init(allocator);
defer reports.deinit();
while (lines.next()) |line| {
if (line.len == 0) continue;
var report = std.ArrayList(u32).init(allocator);
var words = std.mem.split(u8, line, " ");
while (words.next()) |word| {
try report.append(try std.fmt.parseInt(u32, word, 10));
}
try reports.append(report);
}
var safe: u32 = 0;
for (reports.items) |report| {
var is_safe = false;
for ([_]bool{ false, true }) |increasing| for (0..report.items.len) |skipped| {
const first: u32 = if (skipped == 0) 1 else 0;
var prev = report.items[first];
for (first + 1..report.items.len) |i| {
if (i == skipped) continue;
const curr = report.items[i];
if ((prev < curr) != increasing or prev == curr or @max(prev, curr) - @min(prev, curr) > 3) {
break;
}
prev = curr;
} else {
is_safe = true;
}
};
if (is_safe) safe += 1;
// std.debug.print("{any} is {s}safe\n", .{ report.items, if (is_safe) "" else "un" });
}
return safe;
}
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