Wrote program for Day 63

README.md

@@ -109,7 +109,7 @@ We encourage you to share your progress and ask questions in the Discussions sec
 | Day #60       | [A Game Of Threes](https://github.com/LiveGray/100-Days-Of-Rust/tree/main/Week-09/Day-60_A-Game-Of-Thrones)                      | :white_check_mark:      |
 | Day #61       | [Write A Web Crawler](https://github.com/LiveGray/100-Days-Of-Rust/tree/main/Week-09/Day-61_Write-A-Web-Crawler)                   | :white_check_mark:      |
 | Day #62       | [Funny Plant](https://github.com/LiveGray/100-Days-Of-Rust/tree/main/Week-09/Day-62_Funny-Plant)                           | :white_check_mark:      |
-| Day #63       | [The Rabbit Problem](https://github.com/LiveGray/100-Days-Of-Rust/tree/main/Week-09/Day-63_The-Rabbit-Problem)                    | :white_large_square:      |
+| 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_large_square:      |
 | Day #65       | [ISBN Validator](https://github.com/LiveGray/100-Days-Of-Rust/tree/main/Week-10/Day-65_ISBN-Validator)                        | :white_large_square:      |
 | Day #66       | [ISBN Generator](https://github.com/LiveGray/100-Days-Of-Rust/tree/main/Week-10/Day-66_ISBN-Generator)                        | :white_large_square:      |

Week-09/Day-63_The-Rabbit-Problem/day63/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "day63"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

Week-09/Day-63_The-Rabbit-Problem/day63/src/lib.rs

@@ -0,0 +1,47 @@
+pub fn rabbit_problem(male: usize, female: usize, needed: usize) -> Result<(usize, usize), String> {
+    if female == 0 {
+        return Err("The number of initial female rabbits must be positive".to_owned());
+    }
+    let mut females = [0usize; 97];
+    let mut males = [0usize; 97];
+    let mut count = male + female;
+    let mut months = 1;
+    let mut deaths = 0;
+    females[3] = female;
+    males[3] = male;
+    while count < needed {
+        let mut males_newborns = 0;
+        let mut females_newborns = 0;
+        let mut current_month_deaths = 0;
+
+        for i in (0..97).rev() {
+            if i >= 4 {
+                males_newborns += 5 * females[i];
+                females_newborns += 9 * females[i];
+            }
+            if i == 96 {
+                current_month_deaths = males[i] + females[i];
+                males[i] = 0;
+                females[i] = 0;
+                continue;
+            }
+            males[i + 1] = males[i];
+            females[i + 1] = females[i];
+        }
+
+        count = match count.checked_add(
+            match males_newborns.checked_add(females_newborns - current_month_deaths) {
+                Some(x) => x,
+                None => needed,
+            },
+        ) {
+            Some(x) => x,
+            None => needed,
+        };
+        deaths += current_month_deaths;
+        females[0] = females_newborns;
+        males[0] = males_newborns;
+        months += 1;
+    }
+    Ok((months, deaths))
+}

Week-09/Day-63_The-Rabbit-Problem/day63/src/main.rs

@@ -0,0 +1,56 @@
+use std::{
+    io::{self, Write},
+    num::ParseIntError,
+    process::exit,
+};
+
+use day63::rabbit_problem;
+
+fn read_usize() -> Result<usize, ParseIntError> {
+    let mut buffer = String::new();
+    io::stdin().read_line(&mut buffer).unwrap();
+    buffer.trim().parse()
+}
+
+fn main() {
+    print!("Enter the number of male rabbits: ");
+    io::stdout().flush().unwrap();
+    let male = match read_usize() {
+        Ok(x) => x,
+        Err(e) => {
+            eprintln!("{e}");
+            exit(1);
+        }
+    };
+
+    print!("Enter the number of female rabbits: ");
+    io::stdout().flush().unwrap();
+    let female = match read_usize() {
+        Ok(x) => x,
+        Err(e) => {
+            eprintln!("{e}");
+            exit(1);
+        }
+    };
+
+    print!("Enter the needed number of rabbits: ");
+    io::stdout().flush().unwrap();
+    let needed = match read_usize() {
+        Ok(x) => x,
+        Err(e) => {
+            eprintln!("{e}");
+            exit(1);
+        }
+    };
+
+    let (months, dead) = match rabbit_problem(male, female, needed) {
+        Ok(x) => x,
+        Err(e) => {
+            eprintln!("{e}");
+            exit(1);
+        }
+    };
+    println!(
+        "After {months} months the rabbits dominated the world, during which {dead} rabbits died"
+    );
+}

Week-09/Day-63_The-Rabbit-Problem/day63/tests/examples.rs

@@ -0,0 +1,14 @@
+#[cfg(test)]
+mod examples {
+    use day63::rabbit_problem;
+
+    #[test]
+    fn example1() {
+        assert_eq!(rabbit_problem(2, 4, 1000000000).unwrap().0, 32)
+    }
+
+    #[test]
+    fn example2() {
+        assert_eq!(rabbit_problem(2, 4, 15000000000).unwrap().0, 36)
+    }
+}