1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
|
public class LetterCombinationsOfAPhoneNumber {
public List<String> letterCombinations(String digits) {
List<String> result = new ArrayList<String>();
if (digits == null || digits.isEmpty()) {
return result;
}
helper(new StringBuilder(), result, 0, digits);
return result;
}
private void helper(StringBuilder sb, List<String> result, int index, String digits) {
if (index == digits.length()) {
result.add(sb.toString());
return;
}
String s = getString().get(digits.charAt(index));
for (int i = 0; i < s.length(); i++) {
sb.append(s.charAt(i));
helper(sb, result, index + 1, digits);
sb.deleteCharAt(sb.length() - 1);
}
}
private Map<Character, String> getString() {
Map<Character, String> map = new HashMap<Character, String>();
map.put('2', "abc");
map.put('3', "def");
map.put('4', "ghi");
map.put('5', "jkl");
map.put('6', "mno");
map.put('7', "pqrs");
map.put('8', "tuv");
map.put('9', "wxyz");
map.put('0', " ");
return map;
}
@Test
public void test() {
List<String> result = letterCombinations("23");
}
}
|