leetcode-17. Letter Combinations of a Phone Number

leetcode-17. Letter Combinations of a Phone Number

题目：

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”].

这个是讨论里的答案比我原先的答案写的好。我原先是把所有元素都清空了。在做的。这一个利用了LinkedList的特性做了一个FIFO。程序看起来比较简洁一些。值得学习。LinkedList用的不多一时间还真没想起来。

答案来源

public class Solution {
    private String[] mapping = new String[] {"0", "1", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
    public List<String> letterCombinations(String digits) {
    LinkedList<String> ans = new LinkedList<String>();
    if(digits.length()<1) return ans;
    ans.add("");
    for(int i =0; i<digits.length();i++){
        int x = digits.charAt(i) - '0';
        while(ans.peek().length()==i){
            String t = ans.remove();
            for(char s : mapping[x].toCharArray())
                ans.add(t+s);
        }
    }
    return ans;
    }
}