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| class Solution {
private static Map<Integer, char[]> numCharset = new HashMap<>();
static {
numCharset.put(2, new char[] { 'a', 'b', 'c' });
numCharset.put(3, new char[] { 'd', 'e', 'f' });
numCharset.put(4, new char[] { 'g', 'h', 'i' });
numCharset.put(5, new char[] { 'j', 'k', 'l' });
numCharset.put(6, new char[] { 'm', 'n', 'o' });
numCharset.put(7, new char[] { 'p', 'q', 'r', 's' });
numCharset.put(8, new char[] { 't', 'u', 'v' });
numCharset.put(9, new char[] { 'w', 'x', 'y', 'z' });
}
public List<String> letterCombinations(String digits) {
List<String> result = new ArrayList<>();
if (digits == null || digits.length() == 0)
return result;
helper(result, "", digits, 0);
return result;
}
private void helper(List<String> result, String current, String digits, int pos) {
if (pos == digits.length()) {
result.add(current);
return;
}
int currentDigit = digits.charAt(pos) - '0';
char[] availableChars = numCharset.get(currentDigit);
for (char availableChar : availableChars) {
String newString = current + availableChar;
helper(result, newString, digits, pos + 1);
}
}
}
|
