Wrote program for Day 66

README.md

@@ -112,7 +112,7 @@ We encourage you to share your progress and ask questions in the Discussions sec
 | Day #63       | [The Rabbit Problem](https://github.com/LiveGray/100-Days-Of-Rust/tree/main/Week-09/Day-63_The-Rabbit-Problem)                    | :white_check_mark:      |
 | Day #64       | [First Recurring Character](https://github.com/LiveGray/100-Days-Of-Rust/tree/main/Week-10/Day-64_First-Recurring-Character)             | :white_check_mark:      |
 | Day #65       | [ISBN Validator](https://github.com/LiveGray/100-Days-Of-Rust/tree/main/Week-10/Day-65_ISBN-Validator)                        | :white_check_mark:      |
-| Day #66       | [ISBN Generator](https://github.com/LiveGray/100-Days-Of-Rust/tree/main/Week-10/Day-66_ISBN-Generator)                        | :white_large_square:      |
+| Day #66       | [ISBN Generator](https://github.com/LiveGray/100-Days-Of-Rust/tree/main/Week-10/Day-66_ISBN-Generator)                        | :white_check_mark:      |
 | Day #67       | [Color Maze](https://github.com/LiveGray/100-Days-Of-Rust/tree/main/Week-10/Day-67_Color-Maze)                            | :white_large_square:      |
 | Day #68       | [Clarence The Slow Typist](https://github.com/LiveGray/100-Days-Of-Rust/tree/main/Week-10/Day-68_Clarence-The-Slow-Typist)              | :white_large_square:      |
 | Day #69       | [Garage Door Opener](https://github.com/LiveGray/100-Days-Of-Rust/tree/main/Week-10/Day-69-Garage-Door-Opener)                    | :white_large_square:      |

Week-10/Day-66_ISBN-Generator/day66/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "day66"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+lazy_static = "1.5.0"

Week-10/Day-66_ISBN-Generator/day66/src/lib.rs

@@ -0,0 +1,83 @@
+use std::sync::{Arc, Mutex};
+use std::time::{SystemTime, UNIX_EPOCH};
+
+lazy_static::lazy_static! {
+    static ref RNG: Arc<Mutex<Rng>> = Arc::new(Mutex::new(Rng::new()));
+}
+
+pub fn isbn_generator() -> String {
+    let mut rng = RNG.lock().unwrap();
+    let mut partial_isbn = rng.random_number(1e8 as u128, 1e9 as u128);
+    let mut isbn = partial_isbn.to_string();
+
+    let mut val = 0;
+    let mut counter = 1;
+    while partial_isbn > 0 {
+        counter += 1;
+        val += partial_isbn % 10 * counter;
+        partial_isbn /= 10;
+    }
+
+    isbn.push(if (val + 10) % 11 == 0 {
+        'X'
+    } else if val % 11 == 0 {
+        '0'
+    } else {
+        (11 - val % 11).to_string().chars().last().unwrap()
+    });
+
+    isbn
+}
+
+pub fn isbn_validator(digits: &str) -> Result<bool, String> {
+    if digits.len() != 10 {
+        return Err("Invalid length for the ISBN".to_owned());
+    }
+    let mut val: usize = 0;
+    for (i, digit) in digits[..digits.len() - 1].chars().enumerate() {
+        if !digit.is_ascii_digit() {
+            return Err("Only digits allowed".to_owned());
+        }
+        val += (digit as u8 - b'0') as usize * (10 - i);
+    }
+    let digit = digits.chars().last().unwrap();
+    if digit == 'X' {
+        val += 10;
+    } else {
+        val += (digit as u8 - b'0') as usize;
+    }
+    Ok(val % 11 == 0)
+}
+
+pub struct Rng {
+    seed: u128,
+}
+
+impl Rng {
+    pub fn new() -> Rng {
+        let time_since_epoch = SystemTime::now()
+            .duration_since(UNIX_EPOCH)
+            .expect("Error in getting time")
+            .as_millis();
+        Rng {
+            seed: time_since_epoch,
+        }
+    }
+
+    fn linear_congruent_generator(&mut self, a: u128, c: u128, m: u128) -> u128 {
+        let result = (a * self.seed + c) % m;
+        self.seed = result;
+        result
+    }
+
+    pub fn random_number(&mut self, from: u128, to: u128) -> u128 {
+        let random_number = self.linear_congruent_generator(1103515245, 12345, 2u128.pow(31));
+        (random_number % (to - from)) + from
+    }
+}
+
+impl Default for Rng {
+    fn default() -> Self {
+        Self::new()
+    }
+}

Week-10/Day-66_ISBN-Generator/day66/src/main.rs

@@ -0,0 +1,14 @@
+use std::io::{self, Write};
+
+use day66::isbn_generator;
+
+fn main() {
+    let mut _buffer = String::new();
+    println!("Press <enter> to generate a new ISBN, or <c-C> to exit the program");
+    loop {
+        let isbn = isbn_generator();
+        print!("{isbn}");
+        io::stdout().flush().unwrap();
+        io::stdin().read_line(&mut _buffer).unwrap();
+    }
+}

Week-10/Day-66_ISBN-Generator/day66/tests/checker.rs

@@ -0,0 +1,27 @@
+#[cfg(test)]
+mod checker {
+    use day66::*;
+
+    fn check() {
+        assert!(isbn_validator(isbn_generator().trim()).unwrap());
+    }
+
+    #[test]
+    fn gen1() {
+        check();
+    }
+
+    #[test]
+    fn gen10() {
+        for _ in 0..10 {
+            check();
+        }
+    }
+
+    #[test]
+    fn gen100() {
+        for _ in 0..100 {
+            check();
+        }
+    }
+}