letter combinations of a phone number

fishercoder1534 · fishercoder1534 · commit 72327ad09857 · 2016-10-03T21:09:35.000-07:00
diff --git a/MEDIUM/src/medium/LetterCombinationsofaPhoneNumber.java b/MEDIUM/src/medium/LetterCombinationsofaPhoneNumber.java
@@ -0,0 +1,34 @@
+package medium;
+import java.util.*;
+/**
+ * Created by fishercoder1534 on 10/3/16.
+ */
+public class LetterCombinationsofaPhoneNumber {
+
+    public List<String> letterCombinations(String digits) {
+        String[] digits2Letters = new String[]{"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
+
+        List<String> result = new ArrayList();
+        if(digits.length() == 0) return result;
+
+        result.add("");//this line is important, otherwise result is empty and Java will default it to an empty String
+        for(int i = 0; i < digits.length(); i++){
+            result = combine(digits2Letters[digits.charAt(i)-'0'], result);
+        }
+
+        return result;
+    }
+
+    List<String> combine(String letters, List<String> result){
+        List<String> newResult = new ArrayList();
+
+        for(int i = 0; i < letters.length(); i++){
+            for(String str : result){
+                newResult.add(str + letters.charAt(i));
+            }
+        }
+
+        return newResult;
+    }
+
+}
