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"].
Note:
Although the above answer is in lexicographical order, your answer could be in any order you want.
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java code:
public class Solution {
public List<String> letterCombinations(String digits) {
String[] mappings = {"0","1","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
LinkedList<String> ans = new LinkedList<String>();
if(digits.length() == 0) return ans;
ans.add("");
for(int i=0;i<digits.length();i++) {
int num = digits.charAt(i)-'0';
while(ans.peek().length() == i) {
String t = ans.remove();
for(char c : mappings[num].toCharArray()) {
ans.add(t+c);
}
}
}
return ans;
}
}LeetCode:Letter Combinations of a Phone Number
原文：http://blog.csdn.net/itismelzp/article/details/51530965