1. 就是深搜沾谜。深搜三原則：終止條件，當(dāng)下操作胀莹，回退基跑。
2. 寫完發(fā)現(xiàn)，這題早就做過了嗜逻。
代碼如下：?
class?Solution?{
????public?List<String>?letterCombinations(String?digits)?{
????????if(null==digits?||?digits.equals("")){
????????????return?new?ArrayList<String>();
????????}
????????Map<Character,?String>?map?=?new?HashMap<Character,?String>();
????????//?map.put('1',)
????????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");
????????List<String>?result?=?new?ArrayList<String>();
????????StringBuffer?sb?=?new?StringBuffer("");
????????letterCombinationsHelp(result,?map,?digits,?0,?sb);
????????return?result;
????}
????void?letterCombinationsHelp(List<String>?result,?Map<Character,?String>?map,?String?digits,int?index,?StringBuffer?sb??){
????????if(index?==?digits.length()?){
????????????result.add(sb.toString());
????????????return;
????????}
????????String?letterList?=?map.get(digits.charAt(index));
????????for(int?i?=?0;?i?<?letterList.length();?i++){
????????????sb.append(letterList.charAt(i));
????????????letterCombinationsHelp(result,?map,?digits,?index+1,?sb);
????????????sb.deleteCharAt(index);
????????}
????}
}
