add initial data

0013-roman-to-integer/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"

0013-roman-to-integer/Cargo.toml

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

0013-roman-to-integer/src/main.rs

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+static ROMAN_VALUES: [(i32, &str); 13] = [
+    (1, "I"),
+    (4, "IV"),
+    (5, "V"),
+    (9, "IX"),
+    (10, "X"),
+    (40, "XL"),
+    (50, "L"),
+    (90, "XC"),
+    (100, "C"),
+    (400, "CD"),
+    (500, "D"),
+    (900, "CM"),
+    (1000, "M"),
+];
+
+pub fn roman_to_int(s: String) -> i32 {
+    let mut s = s;
+
+    let mut result = 0;
+
+    for (num, letters) in ROMAN_VALUES {
+        loop {
+            let left = s.len().saturating_sub(letters.len());
+            let part = &s[left..];
+
+            if part == letters {
+                result += num;
+                s.truncate(left);
+            } else {
+                break;
+            }
+        }
+    }
+
+    result
+}
+
+fn main() {}
+
+#[cfg(test)]
+mod tests {
+    use crate::roman_to_int;
+
+    #[test]
+    fn test_1() {
+        assert_eq!(roman_to_int("MMMDCCXLIX".to_string()), 3749);
+    }
+
+    #[test]
+    fn test_2() {
+        assert_eq!(roman_to_int("LVIII".to_string()), 58);
+    }
+
+    #[test]
+    fn test_3() {
+        assert_eq!(roman_to_int("MCMXCIV".to_string()), 1994);
+    }
+}