标签：leetcode   算法   

问题描述：

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.

基本思想;

组合所有情况。

代码：

 public List<String> letterCombinations(String digits) {  //Java
        List<String> result = new ArrayList<String>();
        result.add("");
        if(digits.length() == 0)
            return result;
        Map<Integer,String> nums = new HashMap<Integer,String>();
        nums.put(2,"abc");
        nums.put(3,"def");
        nums.put(4,"ghi");
        nums.put(5,"jkl");
        nums.put(6,"mno");
        nums.put(7,"pqrs");
        nums.put(8,"tuv");
        nums.put(9,"wxyz");
        
        Set<String> comb = new HashSet<String>();
        for(int i = 0; i < digits.length(); i++){
            Set<String> temp = new HashSet<String>();
            if(comb.size() == 0){
                String str = nums.get(Integer.valueOf(digits.substring(i,i+1)));
                for(int j = 0; j < str.length(); j++){
                    temp.add(str.substring(j,j+1));
                }
            }
            else{
                String str = nums.get(Integer.valueOf(digits.substring(i,i+1)));
                for(int j = 0; j < str.length(); j++){
                    String ch = str.substring(j,j+1);
                    for(String item: comb){
                        temp.add(item+ch);
                    }
                }
            }
            comb.clear();
            comb = temp;
            
        }
        List<String> list = new ArrayList<String>();
        for(String item: comb){
            list.add(item);
        }
        return list;
    }

[leetcode]Letter Combinations of a Phone Number

标签：leetcode   算法   

原文地址：http://blog.csdn.net/chenlei0630/article/details/41811235