add initial data

0012-integer-to-roman/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "leetcode"
+version = "0.1.0"

0012-integer-to-roman/Cargo.toml

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+[package]
+name = "leetcode"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

0012-integer-to-roman/src/main.rs

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+static ROMAN_VALUES: [(i32, &str); 13] = [
+    (1000, "M"),
+    (900, "CM"),
+    (500, "D"),
+    (400, "CD"),
+    (100, "C"),
+    (90, "XC"),
+    (50, "L"),
+    (40, "XL"),
+    (10, "X"),
+    (9, "IX"),
+    (5, "V"),
+    (4, "IV"),
+    (1, "I"),
+];
+
+pub fn int_to_roman(num: i32) -> String {
+    let mut num = num;
+
+    let mut buf = String::new();
+
+    for (subtrahend, letters) in ROMAN_VALUES {
+        while let Some(n) = num.checked_sub(subtrahend)
+            && n >= 0
+        {
+            num = n;
+            buf.push_str(letters);
+        }
+    }
+
+    buf
+}
+
+fn main() {}
+
+#[cfg(test)]
+mod tests {
+    use crate::int_to_roman;
+
+    #[test]
+    fn test_1() {
+        assert_eq!(int_to_roman(3749), "MMMDCCXLIX");
+    }
+
+    #[test]
+    fn test_2() {
+        assert_eq!(int_to_roman(58), "LVIII");
+    }
+
+    #[test]
+    fn test_3() {
+        assert_eq!(int_to_roman(1994), "MCMXCIV");
+    }
+}