Merge pull request #454 from namita0210/Day-19-Q3

Day 19 Q3

Day-19/q3-Letter Combinations of a Phone Number/namita0210_java.java

@@ -0,0 +1,44 @@
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class namita0210_java {
+
+    public static List<String> letterCombinations(String digits) {
+        List<String> result = new ArrayList<>();
+        if (digits == null || digits.length() == 0) {
+            return result;
+        }
+
+        Map<Character, String> digitToLetters = new HashMap<>();
+        digitToLetters.put('2', "abc");
+        digitToLetters.put('3', "def");
+        digitToLetters.put('4', "ghi");
+        digitToLetters.put('5', "jkl");
+        digitToLetters.put('6', "mno");
+        digitToLetters.put('7', "pqrs");
+        digitToLetters.put('8', "tuv");
+        digitToLetters.put('9', "wxyz");
+
+        generateCombinations(result, digits, digitToLetters, "", 0);
+
+        return result;
+    }
+
+    private static void generateCombinations(List<String> result, String digits, Map<Character, String> digitToLetters, String current, int index) {
+        if (index == digits.length()) {
+            result.add(current);
+            return;
+        }
+
+        char digit = digits.charAt(index);
+        String letters = digitToLetters.get(digit);
+
+        for (char letter : letters.toCharArray()) {
+            generateCombinations(result, digits, digitToLetters, current + letter, index + 1);
+        }
+    }
+
+
+}