Letter Combinations of a Phone Number

最新推荐文章于 2024-01-18 13:57:19 发布

mk476734929

最新推荐文章于 2024-01-18 13:57:19 发布

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本文链接：https://blog.youkuaiyun.com/mk476734929/article/details/87823520

本文介绍了一种使用深度优先搜索(DFS)算法解决电话号码对应字母组合问题的方法。通过递归调用，从电话按键映射中找出所有可能的字母组合。

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Given a string containing digits from 2-9 inclusive, 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. Note that 1 does not map to any letters.

Example:

Input: "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.

解法：

DFS，关键在于递归的写法。一开始没想明白，后来套用树的图就想通了。

public class Solution {
    
    
    
    public List<String> letterCombinations(String digits) {
        
        
        // 建立映射表
        String[] phone = {" ", " ", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
        List<String> res = new ArrayList<String>();
        if(digits.length()==0)return res;
        dfs(0,digits.length(),"",phone,digits,res);
        return res;
    }
    
    public void dfs(int x,int length,String str,String[] phone, String digits,List<String> res){
        
        if(x == length){
            //找到一个答案，返回
            res.add(str);
            return;
        }
        int d = digits.charAt(x)-'0';
        for(int i=0;i<phone[d].length();i++){
            
            dfs(x+1,length,str+phone[d].charAt(i),phone,digits,res);
            
        }
        
    }
    
}