100 exercises to learn Rust

exercises/02_basic_calculator/09_saturating/src/lib.rs

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+pub fn factorial(n: u32) -> u32 {
+    let mut result = 1;
+    for i in 1..=n {
+        // Use saturating multiplication to stop at the maximum value of u32
+        // rather than overflowing and wrapping around
+        result *= i;
+    }
+    result
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::factorial;
+
+    #[test]
+    fn twentieth() {
+        assert_eq!(factorial(20), u32::MAX);
+    }
+
+    #[test]
+    fn first() {
+        assert_eq!(factorial(0), 1);
+    }
+
+    #[test]
+    fn second() {
+        assert_eq!(factorial(1), 1);
+    }
+
+    #[test]
+    fn third() {
+        assert_eq!(factorial(2), 2);
+    }
+
+    #[test]
+    fn fifth() {
+        assert_eq!(factorial(5), 120);
+    }
+}