Letter Combinations of a Phone Number

Author: Kilerd

src/letter_combinations_of_a_phone_number.rs

@@ -0,0 +1,81 @@
+/// @number 17
+/// @title Letter Combinations of a Phone Number
+/// @url https://leetcode.com/problems/letter-combinations-of-a-phone-number/
+/// @difficulty medium
+
+
+struct Solution;
+
+impl Solution {
+    pub fn letter_combinations(digits: String) -> Vec<String> {
+        let len = digits.len();
+        if len < 1 { return vec![]; };
+
+        let x = &digits[len - 1..];
+        let letter_chars = match x {
+            "2" => vec!["a", "b", "c"],
+            "3" => vec!["d", "e", "f"],
+            "4" => vec!["g", "h", "i"],
+            "5" => vec!["j", "k", "l"],
+            "6" => vec!["m", "n", "o"],
+            "7" => vec!["p", "q", "r", "s"],
+            "8" => vec!["t", "u", "v"],
+            "9" => vec!["w", "x", "y", "z"],
+            _ => vec![]
+        };
+        let letter_chars_len = letter_chars.len();
+
+        if len == 1 {
+            return letter_chars.iter().map(|c| String::from(*c)).collect::<Vec<String>>();
+        }
+
+        if letter_chars_len < 1 {
+            return Solution::letter_combinations(String::from(&digits[..len - 1]));
+        }
+
+
+        let prefix = Solution::letter_combinations(String::from(&digits[..len - 1]));
+
+        let mut ret = vec![];
+        if prefix.len() > 0 {
+            for x in prefix {
+                for y in letter_chars.clone() {
+                    ret.push(format!("{}{}", x.clone(), y.clone()));
+                }
+            }
+            ret
+        } else {
+            letter_chars.iter().map(|c| String::from(*c)).collect::<Vec<String>>()
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use crate::letter_combinations_of_a_phone_number::Solution;
+    use std::vec::Vec;
+
+    #[test]
+    fn should_work_with_one_letter() {
+        assert_eq!(
+            vec!["a", "b", "c"].iter().map(|c| String::from(*c)).collect::<Vec<String>>(),
+            Solution::letter_combinations("2".into())
+        );
+    }
+
+    #[test]
+    fn should_work_with_two_letter() {
+        assert_eq!(
+            vec!["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].iter().map(|c| String::from(*c)).collect::<Vec<String>>(),
+            Solution::letter_combinations("23".into())
+        );
+    }
+
+    #[test]
+    fn should_work_with_two_letter_with_invalid_letter() {
+        assert_eq!(
+            vec!["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].iter().map(|c| String::from(*c)).collect::<Vec<String>>(),
+            Solution::letter_combinations("213".into())
+        );
+    }
+}

src/main.rs

@@ -27,4 +27,5 @@ mod string_to_integer_atoi;
 mod palindrome_number;
 mod container_with_most_water;
 mod three_sum;
-mod three_sum_closest;
+mod three_sum_closest;
+mod letter_combinations_of_a_phone_number;