1 files changed, 42 insertions, 0 deletions
diff --git a/rust/rustlings/exercises/18_iterators/iterators4.rs b/rust/rustlings/exercises/18_iterators/iterators4.rs
new file mode 100644
index 0000000..f153786
--- /dev/null
+++ b/rust/rustlings/exercises/18_iterators/iterators4.rs
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+fn factorial(num: u64) -> u64 {
+    // TODO: Complete this function to return the factorial of `num` which is
+    // defined as `1 * 2 * 3 * … * num`.
+    // https://en.wikipedia.org/wiki/Factorial
+    //
+    // Do not use:
+    // - early returns (using the `return` keyword explicitly)
+    // Try not to use:
+    // - imperative style loops (for/while)
+    // - additional variables
+    // For an extra challenge, don't use:
+    // - recursion
+    (1..=num).reduce(|a, b| a * b).unwrap_or(1)
+}
+
+fn main() {
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn factorial_of_0() {
+        assert_eq!(factorial(0), 1);
+    }
+
+    #[test]
+    fn factorial_of_1() {
+        assert_eq!(factorial(1), 1);
+    }
+    #[test]
+    fn factorial_of_2() {
+        assert_eq!(factorial(2), 2);
+    }
+
+    #[test]
+    fn factorial_of_4() {
+        assert_eq!(factorial(4), 24);
+    }
+}