Leetcode17 电话号码的字母组合

最新推荐文章于 2024-09-11 16:32:55 发布

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最新推荐文章于 2024-09-11 16:32:55 发布

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分类专栏： Leetcode

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public List<String> letterCombinations(String digits) {
        List<String> comb = new ArrayList<>();

        Map<Character,String> map = new HashMap<>();
        map.put('2',"abc");
        map.put('3',"def");
        map.put('4',"ghi");
        map.put('5',"jkl");
        map.put('6',"mno");
        map.put('7',"pqrs");
        map.put('8',"tuv");
        map.put('9',"wxyz");

        if(digits.length()==0) return comb;

        backTracking(comb,digits,0,map,new StringBuilder());

        return comb;
    }

    public void backTracking(List<String> list,String digits,int index,Map<Character,String> map,StringBuilder builder){
        if(index==digits.length()){
            list.add(builder.toString());
            return;
        }else{
            char digit = digits.charAt(index);
            String letters=map.get(digit);
            int lettersLen = letters.length();
            for(int i=0;i<lettersLen;i++){
                builder.append(letters.charAt(i));
                backTracking(list,digits,index+1,map,builder);
                builder.deleteCharAt(index);
            }
        } 
        
    }