17. Letter Combinations of a Phone Number

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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全排列非递归实现之一：

 

while(flag <= size){
	            int index = 0;
	            String[] strTemp = new String[strA.length * strB.length];
	            for(int i = 0; i < strA.length; i++){
	               for(int j = 0; j < strB.length; j++){
	                   strTemp[index++] = strA[i] + strB[j];
	               } 
	               
	            }
	           strA = strTemp;
	           if(flag < size){
	               
	               BArr = items[numsArr[flag]-'0'].toCharArray();
	               strB = new String[BArr.length];
	               for(int i = 0; i < BArr.length; i++){
	                   strB[i] = ""+BArr[i];
	               }
	           }else{
	               break;
	           }
	            
	           flag++;
	            
	        }

第二次

public class Solution {
    public List<String> letterCombinations(String digits) {
        List<String> result = new ArrayList<>();
        char[][] items = {{' '}, {' '}, {'a','b','c'},{'d','e','f'},{'g','h','i'},{'j','k','l'},{'m','n','o'},{'p','q','r','s'},{'t','u','v'},{'w','x','y','z'}};
        int index = 0, now = 0;
        while(index < digits.length()){
            now = Integer.valueOf(""+digits.charAt(index++));
            List<String> resultNow = new ArrayList<>();
            if(now != 0 && now != 1){
                for(int i = 0; i < items[now].length; i++){
                    if(result.size() == 0){
                        resultNow.add(""+items[now][i]);
                    }else{
                        for(int j = 0; j < result.size(); j++){
                            resultNow.add(result.get(j) + items[now][i]);
                        }
                    }
                }
                result = resultNow;
            }
            
        }
        
        return result;
    }
}