init

problems/p20/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "p20"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+num-bigint = "0.4.6"

problems/p20/src/main.rs

@@ -0,0 +1,17 @@
+use num_bigint::BigUint;
+
+fn main() {
+    let mut fact = BigUint::from(1u32);
+    for i in 1..=100 {
+        fact *= BigUint::from(i as u32);
+    }
+    let mut sum = BigUint::from(0u32);
+    let ten = BigUint::from(10u32);
+    let zero = BigUint::from(0u32);
+    while fact != zero {
+        sum += &fact % &ten;
+        fact /= &ten;
+    }
+
+    println!("{sum}");
+}