¥17 递归回溯 ¥电话号码的字母组合

好复杂的回溯…
https://leetcode-cn.com/problems/letter-combinations-of-a-phone-number/solution/dian-hua-hao-ma-de-zi-mu-zu-he-by-leetcode-solutio/
在这里插入图片描述

class Solution {
    
    
    public List<String> letterCombinations(String digits) {
    
    
        List<String> combinations = new ArrayList<String>();
        if (digits.length() == 0) {
    
    
            return combinations;
        }
        Map<Character, String> phoneMap = new HashMap<Character, String>() {
    
    {
    
    
            put('2', "abc");
            put('3', "def");
            put('4', "ghi");
            put('5', "jkl");
            put('6', "mno");
            put('7', "pqrs");
            put('8', "tuv");
            put('9', "wxyz");
        }};
        backtrack(combinations, phoneMap, digits, 0, new StringBuffer());
        return combinations;
    }

    public void backtrack(List<String> combinations, Map<Character, String> phoneMap, String digits, int index, StringBuffer combination) {
    
    
        if (index == digits.length()) {
    
    
            combinations.add(combination.toString());
        } else {
    
    
            char digit = digits.charAt(index);
            String letters = phoneMap.get(digit);
            int lettersCount = letters.length();
            for (int i = 0; i < lettersCount; i++) {
    
    
                combination.append(letters.charAt(i));
                backtrack(combinations, phoneMap, digits, index + 1, combination);
                combination.deleteCharAt(index);
            }
        }
    }
}

作者:LeetCode-Solution
链接:https://leetcode-cn.com/problems/letter-combinations-of-a-phone-number/solution/dian-hua-hao-ma-de-zi-mu-zu-he-by-leetcode-solutio/
来源:力扣(LeetCode)
著作权归作者所有。商业转载请联系作者获得授权,非商业转载请注明出处。

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转载自blog.csdn.net/qq_41557627/article/details/114336492