leetcode17.txt

//Java

class Solution {
    public static List<String> letterCombinations(String digits) {
    	String[] digitletter = {"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"}; 注意数组初始化的方式
    	List<String> res = new ArrayList<String>();
    	if(digits.length() == 0) return res;
    	res.add("");   //必须先加入“” 才能有后续的叠加
    	for(int i = 0;i < digits.length();i++) {
    		res = combination(digitletter[digits.charAt(i) - '0'], res);
    	}
    	return res;
    }
    
    public static List<String> combination(String digits,List<String> l){
    	List<String> result = new ArrayList<>();
    	for(int i = 0;i < digits.length();i++) {
    		for(String x:l) {                                   //若按照下标索取，则需要用l.get()，来表示ArrayList中的元素
    			result.add(x + digits.charAt(i));
    		}
    	}
    	return result;
    }
}