040 ok

040/main.rs

@@ -0,0 +1,23 @@
+use std::str::FromStr;
+
+fn ts(k: usize, s: &String) -> u32 {
+    u32::from_str(s.chars().nth(k).unwrap().to_string().as_str()).unwrap()
+}
+
+fn main() {
+    let mut res = String::from("0");
+    let mut k = 1usize;
+    while res.len() < 1000001 {
+        res.push_str(k.to_string().as_str());
+        k += 1;
+    }
+    
+    println!("{}", ts(9, &res));
+    let mut prod = 1;
+    let mut i = 1;
+    while i <= 1000000 {
+        prod *= ts(i, &res);
+        i *= 10;
+    }
+    println!("{}", prod);
+}