add letter_combinations

src/letter_combinations_of_a_phone_number.rs

@@ -0,0 +1,42 @@
+pub fn letter_combinations(digits: String) -> Vec<String> {
+    if digits.is_empty() {
+        return vec![];
+    }
+    let mut result = Vec::<String>::new();
+    let map = ["abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"];
+    let digits = digits
+        .as_bytes()
+        .iter()
+        .map(|&item| {
+            let index = (item as char).to_digit(10).unwrap() - 2;
+            map[index as usize].to_owned()
+        })
+        .collect::<Vec<String>>();
+    for item in digits {
+        if result.is_empty() {
+            result = item.chars().map(|c| c.to_string()).collect::<Vec<String>>();
+            continue;
+        }
+        let mut temp_vec: Vec<String> = Vec::<String>::new();
+        for cur in result {
+            for char in item.chars() {
+                temp_vec.push(format!("{cur}{char}"));
+            }
+        }
+        result = temp_vec;
+    }
+    result
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn example_1() {
+        assert_eq!(
+            vec!["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"],
+            letter_combinations("23".to_owned())
+        );
+    }
+}

src/lib.rs

@@ -19,4 +19,5 @@ pub mod repeated_character;
 pub mod best_time_to_buy_and_sell_stock;
 pub mod maximum_different_between_increasing_elements;
 pub mod count_submatrices_with_all_ones;
-pub mod jump_game;
+pub mod jump_game;
+pub mod letter_combinations_of_a_phone_number;