[Leetcode] Letter Combinations of a Phone Number (Java)

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于 2014-01-06 11:26:56 发布

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分类专栏： Leetcode 文章标签： leetcode

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本文介绍了一种通过深度优先搜索（DFS）算法将数字字符串转换为对应的字母组合的方法。详细解释了数字到字母的映射规则，并通过实例演示了算法的实现过程。

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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.

DFS

public class Solution {
	private static final String[] number ={"abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
	private ArrayList<String> res ;
	public ArrayList<String> letterCombinations(String digits) {
		res = new ArrayList<String>();
		print(digits, 0,"");	
		if(res.size()==0)
			res.add("");
		return res;
	}
	private void print(String digits,int index,String s) {
		if(index==digits.length()) {
			res.add(s);
			return;
		}
		for(int i=0;i<number[digits.charAt(index)-'2'].length();i++){
			s+=(number[digits.charAt(index)-'2'].charAt(i));
			print(digits, index+1,s);
			s =s.substring(0,s.length()-1);
		}
	}
}