17. 電話號碼的字母組合 - 力扣（LeetCode）

class Solution {List<String> ans =new LinkedList<>();StringBuilder temp = new StringBuilder();public List<String> letterCombinations(String digits) {if(digits==null || digits.length()==0) return ans;String[] numStrings={"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};df(digits,numStrings,0);return ans;}public void df(String digits,String[] numStrings,int start){if(start==digits.length()){ans.add(temp.toString());return;}String str=numStrings[digits.charAt(start)-'0'];for (int i = 0; i <str.length(); i++) {temp.append(str.charAt(i));df(digits, numStrings, start+1);temp.deleteCharAt(temp.length()-1);}}
}