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LeetCode

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Problem

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.

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Example 1:

Input: digits = "23"
Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]

Example 2:

Input: digits = ""
Output: []

Example 3:

Input: digits = "2"
Output: ["a","b","c"]

Constraints:

  • 0 <= digits.length <= 4
  • digits[i] is a digit in the range [‘2’, ‘9’].

Code

  • valueOf 和 getNumericValue
  • valueOf 会返回数字对应的 ascii 码
public class test {
    public static void main(String [] args){
        char c = '5';

        System.out.println(Character.getNumericValue(c));
        System.out.println(Integer.valueOf(c));

        // String 不会受到影响
        String s = "5";
        System.out.println(Integer.valueOf(s));
    }
}
// 输出
// 5
// 53
// 5

class Solution {
    public List<String> letterCombinations(String digits) {
        if(digits == null || digits.length() == 0) return new ArrayList<>();
        
        Queue<String> queue = new LinkedList<>();
        String[] dict = {"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};

        queue.offer("");
        
        for(int i = 0; i < digits.length(); i++) {
            int index = digits.charAt(i) - '0';
            String curr = dict[index];
            while(queue.peek().length() == i) {
                String temp = queue.poll();
                for(char c : curr.toCharArray()){                  
                    queue.offer(temp + String.valueOf(c));
                }
            }
        }
        
        return new ArrayList<>(queue);
    }
}