public class Solution {
public List<String> letterCombinations(String digits) {
List<String> rst = new ArrayList<String>();
if (digits == null || digits.length() == 0) {
return rst;
}
HashMap<Character, char[]> map = new HashMap<Character, char[]>();
map.put('0', new char[]{});
map.put('1', new char[]{});
map.put('2', new char[]{'a', 'b', 'c'});
map.put('3', new char[]{'d', 'e', 'f'});
map.put('4', new char[]{'g', 'h', 'i'});
map.put('5', new char[]{'j', 'k', 'l'});
map.put('6', new char[]{'m', 'n', 'o'});
map.put('7', new char[]{'p', 'q', 'r', 's'});
map.put('8', new char[]{'t', 'u', 'v'});
map.put('9', new char[]{'w', 'x', 'y', 'z'});
StringBuilder sb = new StringBuilder();
helper(digits, map, sb, rst);
return rst;
}
private void helper(String digits, HashMap<Character, char[]> map, StringBuilder sb, List<String> rst) {
if (sb.length() == digits.length()) {
rst.add(sb.toString());
return;
}
for (char c : map.get(digits.charAt(sb.length()))) {
sb.append(c);
helper(digits, map, sb, rst);
sb.deleteCharAt(sb.length() - 1);
}
}
}
在面试的时候遇到了这道题,问到了一些数组初始化的问题