Given a digit string, return all possible letter combinations that the number could represent.
A mapping of digit to letters (just like on the telephone buttons) is given below.
Input:Digit string "23" Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
解题思路:
依旧是DFS模型~注意把数字 0 - 9存进一个string array里面~
使用stringbuilder比直接用string方便得多啊。。
for循环里面是对array里面的某一个字符串的处理~
直接上代码:
1 public ArrayList<String> letterCombinations(String digits) { 2 String[] map = {"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"}; 3 ArrayList<String> ret = new ArrayList<String>(); 4 StringBuilder str = new StringBuilder(); 5 dfs(digits, map, 0, str, ret); 6 return ret; 7 } 8 public void dfs(String digits, String[] map, int n, StringBuilder str, ArrayList<String> list){ 9 if(n == digits.length()){ 10 list.add(str.toString()); 11 return; 12 } 13 String s = map[digits.charAt(n) - ‘0‘]; 14 for(int i = 0; i < s.length(); i++){ //注意i是小于s.lenght的 15 str.append(s.charAt(i)); 16 dfs(digits, map, n + 1, str, list); 17 str.deleteCharAt(str.length() - 1); 18 } 19 }
Leetcode 17 Letter Combinations of a Phone Number - DFS思想
原文：http://www.cnblogs.com/sherry900105/p/4289594.html