Solve integer-to-roman.

source/integer_to_roman/mod.rs

@@ -0,0 +1,31 @@
+pub fn int_to_roman(number: i32) -> String {
+  let mut result = String::new();
+
+  for (index, digit) in number.to_string().chars().rev().enumerate() {
+    if digit == '0' {
+      continue;
+    }
+
+    let digit = digit.to_digit(10).unwrap() as usize;
+    let magnitude = 10_usize.pow(index as u32);
+
+    let (unit_1, unit_5, unit_10) = match magnitude {
+      1 => ("I", "V", "X"),
+      10 => ("X", "L", "C"),
+      100 => ("C", "D", "M"),
+      1000 => ("M", "", ""),
+      _ => ("", "", ""),
+    };
+
+    result += &match digit {
+      1..=3 => unit_1.repeat(digit),
+      4 => format!("{unit_5}{unit_1}"),
+      5 => unit_5.to_string(),
+      6..=8 => format!("{}{unit_5}", unit_1.repeat(digit - 5)),
+      9 => format!("{unit_10}{unit_1}"),
+      _ => continue,
+    }
+  }
+
+  result.chars().rev().collect()
+}

source/lib.rs

@@ -2,6 +2,7 @@ pub mod add_binary;
 pub mod excel_sheet_column_number;
 pub mod excel_sheet_column_title;
 pub mod implement_strstr;
+pub mod integer_to_roman;
 pub mod isomorphic_strings;
 pub mod length_of_last_word;
 pub mod longest_common_prefix;

tests/integer_to_roman.rs

@@ -0,0 +1,12 @@
+use leetcode::integer_to_roman::int_to_roman;
+
+use test_case::test_case;
+
+#[test_case(0, ""; "minimum")]
+#[test_case(3999, "MMMCMXCIX"; "maximum")]
+#[test_case(1666, "MDCLXVI"; "every character")]
+#[test_case(900, "CM"; "with subtracting")]
+#[test_case(20, "XX"; "without subtracting")]
+fn test_integer_to_roman(input: i32, expected: &str) {
+  assert_eq!(int_to_roman(input), expected);
+}