第49题 Letter Combinations of a Phone Number

最新推荐文章于 2024-01-18 13:57:19 发布

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最新推荐文章于 2024-01-18 13:57:19 发布

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本文介绍了一种算法，用于根据电话按键上的数字到字母映射，返回所有可能的字母组合。例如，输入数字字符串23，输出包含[adaeafbdbebfcdcecf]等所有可能的组合。

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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.

Solution in Java:

public class Solution {
    public List<String> letterCombinations(String digits) {
        
        List<String> result = new ArrayList<String>();
        
        Map<String, String> mapDigi = new HashMap<String, String>();
        mapDigi.put("2", "abc");
        mapDigi.put("3", "def");
        mapDigi.put("4", "ghi");
        mapDigi.put("5", "jkl");
        mapDigi.put("6", "mno");
        mapDigi.put("7", "pqrs");
        mapDigi.put("8", "tuv");
        mapDigi.put("9", "wxyz");
        
        for(int i=0; i<digits.length(); i++){
            String curDigi = ""+digits.charAt(i);
            String curChars = mapDigi.get(curDigi);
            if(result.size()==0){
                for(int j=0; j<curChars.length(); j++){
                    result.add(""+curChars.charAt(j));
                }
            }
            else{
                int curLength = result.size();
                for(int index=0; index<curLength; index++){
                    String curStr = result.get(0);
                    for(int j=0; j<curChars.length(); j++){
                        result.add(curStr+curChars.charAt(j));
                    }
                    result.remove(0);
                }
            }
        }
        return result;<strong>
        
    }
}</strong>

Note: 注意7和9对应4个字母，所以不能直接按3的倍数计算其对应字母。从arraylist中移除第i个元素，用list.remove(i)。每个循环中对list中每个元素，在末尾分别加上该digit所对应的字母，然后将该元素删除。