Add initial solution files for Rustlings exercises and quizzes

- Created empty solution files for various exercises in strings, modules, hashmaps, options, error handling, generics, traits, lifetimes, tests, iterators, smart pointers, threads, macros, clippy, conversions, and quizzes.
- Each solution file contains a main function with a comment indicating that it will be automatically filled after completing the exercise.
- Added a README.md file to provide information about the solutions and their purpose.

exercises/18_iterators/iterators3.rs

@@ -0,0 +1,83 @@
+#[derive(Debug, PartialEq, Eq)]
+enum DivisionError {
+    // Example: 42 / 0
+    DivideByZero,
+    // Only case for `i64`: `i64::MIN / -1` because the result is `i64::MAX + 1`
+    IntegerOverflow,
+    // Example: 5 / 2 = 2.5
+    NotDivisible,
+}
+
+// TODO: Calculate `a` divided by `b` if `a` is evenly divisible by `b`.
+// Otherwise, return a suitable error.
+fn divide(a: i64, b: i64) -> Result<i64, DivisionError> {
+    if b == 0 {
+        Err(DivisionError::DivideByZero)
+    } else if a == i64::MIN && b == -1 {
+        Err(DivisionError::IntegerOverflow)
+    } else if a % b == 0 {
+        Ok(a / b)
+    } else {
+        Err(DivisionError::NotDivisible)
+    }
+}
+
+// TODO: Add the correct return type and complete the function body.
+// Desired output: `Ok([1, 11, 1426, 3])`
+fn result_with_list() -> Result<Vec<i64>, DivisionError> {
+    let numbers = [27, 297, 38502, 81];
+    numbers.into_iter().map(|n| divide(n, 27)).collect()
+}
+
+// TODO: Add the correct return type and complete the function body.
+// Desired output: `[Ok(1), Ok(11), Ok(1426), Ok(3)]`
+fn list_of_results() -> Vec<Result<i64, DivisionError>> {
+    let numbers = [27, 297, 38502, 81];
+    numbers.into_iter().map(|n| divide(n, 27)).collect()
+}
+
+fn main() {
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_success() {
+        assert_eq!(divide(81, 9), Ok(9));
+        assert_eq!(divide(81, -1), Ok(-81));
+        assert_eq!(divide(i64::MIN, i64::MIN), Ok(1));
+    }
+
+    #[test]
+    fn test_divide_by_0() {
+        assert_eq!(divide(81, 0), Err(DivisionError::DivideByZero));
+    }
+
+    #[test]
+    fn test_integer_overflow() {
+        assert_eq!(divide(i64::MIN, -1), Err(DivisionError::IntegerOverflow));
+    }
+
+    #[test]
+    fn test_not_divisible() {
+        assert_eq!(divide(81, 6), Err(DivisionError::NotDivisible));
+    }
+
+    #[test]
+    fn test_divide_0_by_something() {
+        assert_eq!(divide(0, 81), Ok(0));
+    }
+
+    #[test]
+    fn test_result_with_list() {
+        assert_eq!(result_with_list().unwrap(), [1, 11, 1426, 3]);
+    }
+
+    #[test]
+    fn test_list_of_results() {
+        assert_eq!(list_of_results(), [Ok(1), Ok(11), Ok(1426), Ok(3)]);
+    }
+}