leetcode: solve problem 17

leetcode/0017-letter-combinations-of-a-phone-number/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "letter-combinations-of-a-phone-number"
+version = "0.1.0"

leetcode/0017-letter-combinations-of-a-phone-number/Cargo.toml

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+[package]
+name = "letter-combinations-of-a-phone-number"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

leetcode/0017-letter-combinations-of-a-phone-number/readme.md

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+# 17. Letter Combinations of a Phone Number
+
+[Leetcode](https://leetcode.com/problems/letter-combinations-of-a-phone-number/description/)
+
+Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent.
+Return the answer in any order.
+
+A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.

leetcode/0017-letter-combinations-of-a-phone-number/src/lib.rs

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+pub fn letter_combinations(digits: String) -> Vec<String> {
+    let mut res: Vec<String> = vec![];
+
+    for digit in digits.split("") {
+        if digit.is_empty() {
+            continue;
+        }
+
+        let letters = match digit {
+            "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![],
+        };
+
+        if res.is_empty() {
+            for letter in letters {
+                res.push(letter.to_owned());
+            }
+            continue;
+        }
+
+        let mut mu: Vec<String> = vec![];
+        for el in res.iter() {
+            for letter in &letters {
+                mu.push(el.to_owned() + letter);
+            }
+        }
+        res = mu;
+    }
+
+    res
+}
+
+#[cfg(test)]
+mod tests {
+    use super::letter_combinations;
+
+    #[test]
+    fn simple_test() {
+        let expected: Vec<String> = vec!["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"]
+            .iter()
+            .map(|s| s.to_string())
+            .collect();
+        let res = letter_combinations("23".to_string());
+        assert_eq!(res, expected);
+    }
+
+    #[test]
+    fn test_empty_string() {
+        let expected: Vec<String> = vec![];
+        let res = letter_combinations("".to_string());
+        assert_eq!(res, expected);
+    }
+}