diff --git a/Cargo.lock b/Cargo.lock
index bbb840d..07cc225 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,12 +2,62 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "bitflags"
+version = "1.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
+
+[[package]]
+name = "cc"
+version = "1.0.77"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e9f73505338f7d905b19d18738976aae232eb46b8efc15554ffc56deb5d9ebe4"
+
 [[package]]
 name = "cfg-if"
 version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
+[[package]]
+name = "clap"
+version = "4.0.29"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4d63b9e9c07271b9957ad22c173bae2a4d9a81127680962039296abcd2f8251d"
+dependencies = [
+ "bitflags",
+ "clap_derive",
+ "clap_lex",
+ "is-terminal",
+ "once_cell",
+ "strsim",
+ "termcolor",
+ "terminal_size",
+]
+
+[[package]]
+name = "clap_derive"
+version = "4.0.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0177313f9f02afc995627906bbd8967e2be069f5261954222dac78290c2b9014"
+dependencies = [
+ "heck",
+ "proc-macro-error",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "clap_lex"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0d4198f73e42b4936b35b5bb248d81d2b595ecb170da0bac7655c54eedfa8da8"
+dependencies = [
+ "os_str_bytes",
+]
+
 [[package]]
 name = "day01"
 version = "0.1.0"
@@ -34,6 +84,15 @@ dependencies = [
 name = "day03"
 version = "0.1.0"
 
+[[package]]
+name = "day03-gen-problem"
+version = "0.1.0"
+dependencies = [
+ "clap",
+ "lazy_static",
+ "rand",
+]
+
 [[package]]
 name = "day04"
 version = "0.1.0"
@@ -118,6 +177,27 @@ version = "0.1.0"
 name = "day24"
 version = "0.1.0"
 
+[[package]]
+name = "errno"
+version = "0.2.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f639046355ee4f37944e44f60642c6f3a7efa3cf6b78c78a0d989a8ce6c396a1"
+dependencies = [
+ "errno-dragonfly",
+ "libc",
+ "winapi",
+]
+
+[[package]]
+name = "errno-dragonfly"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aa68f1b12764fab894d2755d2518754e71b4fd80ecfb822714a1206c2aab39bf"
+dependencies = [
+ "cc",
+ "libc",
+]
+
 [[package]]
 name = "getrandom"
 version = "0.2.8"
@@ -129,18 +209,121 @@ dependencies = [
  "wasi",
 ]
 
+[[package]]
+name = "heck"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2540771e65fc8cb83cd6e8a237f70c319bd5c29f78ed1084ba5d50eeac86f7f9"
+
+[[package]]
+name = "hermit-abi"
+version = "0.2.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ee512640fe35acbfb4bb779db6f0d80704c2cacfa2e39b601ef3e3f47d1ae4c7"
+dependencies = [
+ "libc",
+]
+
+[[package]]
+name = "io-lifetimes"
+version = "1.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "46112a93252b123d31a119a8d1a1ac19deac4fac6e0e8b0df58f0d4e5870e63c"
+dependencies = [
+ "libc",
+ "windows-sys",
+]
+
+[[package]]
+name = "is-terminal"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "927609f78c2913a6f6ac3c27a4fe87f43e2a35367c0c4b0f8265e8f49a104330"
+dependencies = [
+ "hermit-abi",
+ "io-lifetimes",
+ "rustix",
+ "windows-sys",
+]
+
+[[package]]
+name = "lazy_static"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
+
 [[package]]
 name = "libc"
 version = "0.2.137"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fc7fcc620a3bff7cdd7a365be3376c97191aeaccc2a603e600951e452615bf89"
 
+[[package]]
+name = "linux-raw-sys"
+version = "0.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8f9f08d8963a6c613f4b1a78f4f4a4dbfadf8e6545b2d72861731e4858b8b47f"
+
+[[package]]
+name = "once_cell"
+version = "1.16.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "86f0b0d4bf799edbc74508c1e8bf170ff5f41238e5f8225603ca7caaae2b7860"
+
+[[package]]
+name = "os_str_bytes"
+version = "6.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9b7820b9daea5457c9f21c69448905d723fbd21136ccf521748f23fd49e723ee"
+
 [[package]]
 name = "ppv-lite86"
 version = "0.2.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5b40af805b3121feab8a3c29f04d8ad262fa8e0561883e7653e024ae4479e6de"
 
+[[package]]
+name = "proc-macro-error"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "da25490ff9892aab3fcf7c36f08cfb902dd3e71ca0f9f9517bea02a73a5ce38c"
+dependencies = [
+ "proc-macro-error-attr",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "version_check",
+]
+
+[[package]]
+name = "proc-macro-error-attr"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a1be40180e52ecc98ad80b184934baf3d0d29f979574e439af5a55274b35f869"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "version_check",
+]
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.47"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5ea3d908b0e36316caf9e9e2c4625cdde190a7e6f440d794667ed17a1855e725"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bbe448f377a7d6961e30f5955f9b8d106c3f5e449d493ee1b125c1d43c2b5179"
+dependencies = [
+ "proc-macro2",
+]
+
 [[package]]
 name = "rand"
 version = "0.8.5"
@@ -171,8 +354,158 @@ dependencies = [
  "getrandom",
 ]
 
+[[package]]
+name = "rustix"
+version = "0.36.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cb93e85278e08bb5788653183213d3a60fc242b10cb9be96586f5a73dcb67c23"
+dependencies = [
+ "bitflags",
+ "errno",
+ "io-lifetimes",
+ "libc",
+ "linux-raw-sys",
+ "windows-sys",
+]
+
+[[package]]
+name = "strsim"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "73473c0e59e6d5812c5dfe2a064a6444949f089e20eec9a2e5506596494e4623"
+
+[[package]]
+name = "syn"
+version = "1.0.105"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "60b9b43d45702de4c839cb9b51d9f529c5dd26a4aff255b42b1ebc03e88ee908"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "termcolor"
+version = "1.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bab24d30b911b2376f3a13cc2cd443142f0c81dda04c118693e35b3835757755"
+dependencies = [
+ "winapi-util",
+]
+
+[[package]]
+name = "terminal_size"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cb20089a8ba2b69debd491f8d2d023761cbf196e999218c591fa1e7e15a21907"
+dependencies = [
+ "rustix",
+ "windows-sys",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6ceab39d59e4c9499d4e5a8ee0e2735b891bb7308ac83dfb4e80cad195c9f6f3"
+
+[[package]]
+name = "version_check"
+version = "0.9.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "49874b5167b65d7193b8aba1567f5c7d93d001cafc34600cee003eda787e483f"
+
 [[package]]
 name = "wasi"
 version = "0.11.0+wasi-snapshot-preview1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9c8d87e72b64a3b4db28d11ce29237c246188f4f51057d65a7eab63b7987e423"
+
+[[package]]
+name = "winapi"
+version = "0.3.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c839a674fcd7a98952e593242ea400abe93992746761e38641405d28b00f419"
+dependencies = [
+ "winapi-i686-pc-windows-gnu",
+ "winapi-x86_64-pc-windows-gnu",
+]
+
+[[package]]
+name = "winapi-i686-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
+
+[[package]]
+name = "winapi-util"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "70ec6ce85bb158151cae5e5c87f95a8e97d2c0c4b001223f33a334e3ce5de178"
+dependencies = [
+ "winapi",
+]
+
+[[package]]
+name = "winapi-x86_64-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
+
+[[package]]
+name = "windows-sys"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5a3e1820f08b8513f676f7ab6c1f99ff312fb97b553d30ff4dd86f9f15728aa7"
+dependencies = [
+ "windows_aarch64_gnullvm",
+ "windows_aarch64_msvc",
+ "windows_i686_gnu",
+ "windows_i686_msvc",
+ "windows_x86_64_gnu",
+ "windows_x86_64_gnullvm",
+ "windows_x86_64_msvc",
+]
+
+[[package]]
+name = "windows_aarch64_gnullvm"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "41d2aa71f6f0cbe00ae5167d90ef3cfe66527d6f613ca78ac8024c3ccab9a19e"
+
+[[package]]
+name = "windows_aarch64_msvc"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dd0f252f5a35cac83d6311b2e795981f5ee6e67eb1f9a7f64eb4500fbc4dcdb4"
+
+[[package]]
+name = "windows_i686_gnu"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fbeae19f6716841636c28d695375df17562ca208b2b7d0dc47635a50ae6c5de7"
+
+[[package]]
+name = "windows_i686_msvc"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "84c12f65daa39dd2babe6e442988fc329d6243fdce47d7d2d155b8d874862246"
+
+[[package]]
+name = "windows_x86_64_gnu"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bf7b1b21b5362cbc318f686150e5bcea75ecedc74dd157d874d754a2ca44b0ed"
+
+[[package]]
+name = "windows_x86_64_gnullvm"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09d525d2ba30eeb3297665bd434a54297e4170c7f1a44cad4ef58095b4cd2028"
+
+[[package]]
+name = "windows_x86_64_msvc"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f40009d85759725a34da6d89a94e63d7bdc50a862acf0dbc7c8e488f1edcb6f5"
diff --git a/Cargo.toml b/Cargo.toml
index 6ed8480..c9094dc 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,5 +1,5 @@
 [workspace]
-members = [ "day01", "day01-gen-problem", "day02", "day02-gen-problem", "day03", "day04", "day05", "day06", "day07", "day08", "day09", "day10", "day11", "day12", "day13", "day14", "day15", "day16", "day17", "day18", "day19", "day20", "day21", "day22", "day23", "day24", ]
+members = [ "day01", "day01-gen-problem", "day02", "day02-gen-problem", "day03", "day03-gen-problem", "day04", "day05", "day06", "day07", "day08", "day09", "day10", "day11", "day12", "day13", "day14", "day15", "day16", "day17", "day18", "day19", "day20", "day21", "day22", "day23", "day24", ]
 
 [profile.release]
 #debug = true
diff --git a/day03-gen-problem/Cargo.toml b/day03-gen-problem/Cargo.toml
new file mode 100644
index 0000000..2b78eb0
--- /dev/null
+++ b/day03-gen-problem/Cargo.toml
@@ -0,0 +1,11 @@
+[package]
+name = "day03-gen-problem"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+clap = { version = "4.0.29", features = ["derive", "wrap_help"] }
+lazy_static = "1.4.0"
+rand = { version = "0.8.5", features = ["small_rng"] }
diff --git a/day03-gen-problem/src/main.rs b/day03-gen-problem/src/main.rs
new file mode 100644
index 0000000..b8eb210
--- /dev/null
+++ b/day03-gen-problem/src/main.rs
@@ -0,0 +1,121 @@
+//! Some restrictions
+//! - Number of lines needs to be divisible by three
+//! - Number of chars per line need to be divisible by three
+//! - Every line can be split in two halves sharing exactly one character
+//! - Case matters
+//! - The file can be split into groups of three lines. These three lines share exactly one character
+use clap::Parser;
+use lazy_static::lazy_static;
+use rand::{
+    rngs::SmallRng,
+    seq::{IteratorRandom, SliceRandom},
+    Rng, SeedableRng,
+};
+
+use std::{
+    fs::File,
+    io::{BufWriter, Write},
+    ops::Range,
+    path::PathBuf,
+};
+
+lazy_static! {
+    static ref CHARS: Vec<char> = ('a'..'z').chain('A'..'Z').collect();
+    static ref ARGS: Args = Args::parse();
+}
+
+#[derive(Debug, Parser)]
+#[command(author, version, about, long_about = None)]
+struct Args {
+    #[arg(short = 'n', long, default_value = "20000")]
+    elf_groups: usize,
+    #[arg(short = 'i', long, default_value = "60")]
+    min_line: usize,
+    #[arg(short = 'x', long, default_value = "2000")]
+    max_line: usize,
+    #[arg(short, long)]
+    out_file: PathBuf,
+}
+
+impl Args {
+    pub fn half_line_range(&self) -> Range<usize> {
+        self.min_line..self.max_line
+    }
+}
+
+fn replace_rand<I>(rng: &mut rand::rngs::SmallRng, list: &mut Vec<I>, item: I) {
+    debug_assert!(list.len() > 0);
+    let idx = rng.gen_range(0..list.len());
+    list[idx] = item;
+}
+
+fn gen_triple(rng: &mut rand::rngs::SmallRng) -> [String; 3] {
+    let amounts = ARGS.half_line_range().choose_multiple(rng, 3);
+    // The badge that is shared in this triple
+    let badge: char = *CHARS.choose(rng).unwrap();
+    let mut lines: Vec<String> = amounts
+        .iter()
+        .map(|&amount| {
+            debug_assert!(amount > 0);
+            // The item that is shared between the halves
+            let wrong_between_halves: char = *CHARS
+                .iter()
+                .filter(|&&char| char != badge)
+                .choose(rng)
+                .unwrap();
+            let possible_left = CHARS
+                .iter()
+                .filter(|&&char| char != wrong_between_halves)
+                .filter(|&&char| char != badge)
+                .copied()
+                .choose_multiple(rng, CHARS.len() / 2 - 1);
+            let possible_right: Vec<_> = CHARS
+                .iter()
+                .filter(|&char| !possible_left.contains(char))
+                .copied()
+                .collect();
+            let mut left: Vec<_> = (0..amount)
+                .map(|_| rng.gen_range(0..possible_left.len()))
+                .map(|idx| possible_left[idx])
+                .collect();
+            let mut right: Vec<_> = (0..amount)
+                .map(|_| rng.gen_range(0..possible_right.len()))
+                .map(|idx| possible_right[idx])
+                .collect();
+            debug_assert!(left.len() == amount);
+            debug_assert!(right.len() == amount);
+            // Insert the badge
+            replace_rand(
+                rng,
+                if rand::random() {
+                    &mut left
+                } else {
+                    &mut right
+                },
+                badge,
+            );
+            // Insert the wrong items
+            replace_rand(rng, &mut left, wrong_between_halves);
+            replace_rand(rng, &mut right, wrong_between_halves);
+            debug_assert!(left.len() == right.len());
+            debug_assert!(left.len() == amount);
+            debug_assert!(right.len() == amount);
+            left.into_iter().chain(right).collect::<String>()
+        })
+        .collect();
+    debug_assert!(lines.len() == 3);
+    let third = lines.pop().unwrap();
+    let second = lines.pop().unwrap();
+    let first = lines.pop().unwrap();
+    [first, second, third]
+}
+
+fn main() {
+    let mut outfile = BufWriter::new(File::create(&ARGS.out_file).expect("Can write outfile"));
+    let mut rng = SmallRng::from_rng(rand::thread_rng()).expect("Init rng");
+    (0..ARGS.elf_groups)
+        .flat_map(|_| gen_triple(&mut rng))
+        .inspect(|line| debug_assert!(line.len() % 2 == 0))
+        .for_each(|line| writeln!(outfile, "{line}").expect("Writing works"));
+    outfile.flush().expect("Flushing works");
+}