sol(rust): pset1/credit

rust/pset1/credit/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "credit"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

rust/pset1/credit/README.md

@@ -0,0 +1 @@
+../../../pset1/credit/README.md

rust/pset1/credit/src/lib.rs

@@ -0,0 +1,17 @@
+use std::io::{self, Write};
+
+pub fn get_long(prompt: &str) -> u64 {
+    loop {
+        print!("{prompt}");
+        io::stdout().flush().unwrap();
+
+        let mut input_text = String::new();
+        match io::stdin().read_line(&mut input_text) {
+            Ok(_) => match input_text.trim().parse() {
+                Ok(input_long) => return input_long,
+                Err(_) => continue,
+            },
+            Err(_) => continue,
+        }
+    }
+}

rust/pset1/credit/src/main.rs

@@ -0,0 +1,55 @@
+use credit::get_long;
+
+fn main() {
+    let cc_number = get_long("Number: ");
+    let cc_num_digits = cc_number.to_string().len() as u64;
+
+    if luhn(cc_number) {
+        let leading_digits = cc_number / 10_u64.pow((cc_num_digits - 2) as u32);
+        if cc_num_digits == 15 {
+            if leading_digits == 34 || leading_digits == 37 {
+                println!("AMEX");
+                return;
+            }
+        }
+        if cc_num_digits == 16 {
+            if leading_digits >= 51 && leading_digits <= 55 {
+                println!("MASTERCARD");
+                return;
+            }
+        }
+        if cc_num_digits == 13 || cc_num_digits == 16 {
+            let leading_digits = cc_number / 10_u64.pow((cc_num_digits - 1) as u32);
+            if leading_digits == 4 {
+                println!("VISA");
+                return;
+            }
+        }
+    }
+    println!("INVALID");
+}
+
+fn luhn(cc_number: u64) -> bool {
+    let cc_string = cc_number.to_string();
+    let mut cumsum_one = 0;
+    let mut cumsum_two = 0;
+
+    for (i, val) in cc_string
+        .chars()
+        .rev()
+        .enumerate()
+        .map(|(i, x)| (i, x.to_digit(10).unwrap_or(0)))
+    {
+        if i % 2 != 0 {
+            let mut sum = 2 * val;
+            if sum >= 10 {
+                cumsum_one += sum % 10;
+                sum /= 10;
+            }
+            cumsum_one += sum;
+        } else {
+            cumsum_two += val;
+        }
+    }
+    (cumsum_one + cumsum_two) % 10 == 0
+}