Add 17_Letter_Combinations_of_a_Phone_Number.java

Author: Sean Prashad

Backtracking/17_Letter_Combinations_of_a_Phone_Number.java

@@ -0,0 +1,28 @@
+class Solution {
+ private static final String[] KEYS = new String[] { "", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv",
+ "wxyz" };
+
+ public List<String> letterCombinations(String digits) {
+ if (digits == null || digits.length() == 0) {
+ return Collections.emptyList();
+ }
+
+ List<String> result = new ArrayList<>();
+ dfs(digits, 0, new StringBuilder(), result);
+ return result;
+ }
+
+ private void dfs(String digits, int offset, StringBuilder sb, List<String> result) {
+ if (offset >= digits.length()) {
+ result.add(sb.toString());
+ return;
+ }
+
+ String letters = KEYS[digits.charAt(offset) - '0'];
+ for (int i = 0; i < letters.length(); i++) {
+ sb.append(letters.charAt(i));
+ dfs(digits, offset + 1, sb, result);
+ sb.deleteCharAt(sb.length() - 1);
+ }
+ }
+}