diff --git a/src/problem/mod.rs b/src/problem/mod.rs
index b9a2f30..92659b1 100644
--- a/src/problem/mod.rs
+++ b/src/problem/mod.rs
@@ -164,4 +164,5 @@ mod p433_minimum_genetic_mutation;
 mod p127_word_ladder;
 mod p208_implement_trie_prefix_tree;
 mod p211_design_add_and_search_words_data_structure;
-mod p212_word_search_ii;
\ No newline at end of file
+mod p212_word_search_ii;
+mod p17_letter_combinations_of_a_phone_number;
\ No newline at end of file
diff --git a/src/problem/p17_letter_combinations_of_a_phone_number.rs b/src/problem/p17_letter_combinations_of_a_phone_number.rs
new file mode 100644
index 0000000..c1874ce
--- /dev/null
+++ b/src/problem/p17_letter_combinations_of_a_phone_number.rs
@@ -0,0 +1,57 @@
+/**
+ * [17] Letter Combinations of a Phone Number
+ */
+pub struct Solution {}
+
+
+// submission codes start here
+
+impl Solution {
+    pub fn letter_combinations(digits: String) -> Vec<String> {
+        let mut result = vec![];
+        let digits: Vec<usize> = digits.chars()
+            .map(|c| (c.to_digit(10).unwrap() - 2) as usize)
+            .collect();
+        let mut str = Vec::with_capacity(digits.len());
+        
+        Self::search(&digits, &mut str, &mut result, 0);
+
+        result
+    }
+
+    fn search(digits: &Vec<usize>, str: &mut Vec<char>, result: &mut Vec<String>, pos: usize) {
+        let map = vec![
+            vec!['a', 'b', 'c'],
+            vec!['d', 'e', 'f'],
+            vec!['g', 'h', 'i'],
+            vec!['j', 'k', 'l'],
+            vec!['m', 'n', 'o'],
+            vec!['p', 'q', 'r', 's'],
+            vec!['t', 'u', 'v'],
+            vec!['w', 'x', 'y', 'z'],
+        ];
+
+        if pos >= digits.len() {
+            if !str.is_empty() {
+                result.push(str.iter().collect());
+            }
+            return;
+        }
+        
+        for &c in &map[digits[pos]] {
+            str.push(c);
+            Self::search(digits, str, result, pos + 1);
+            str.pop();
+        }
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_17() {}
+}