LeetCode : Letter Combinations of a Phone Number [java]

最新推荐文章于 2019-06-04 13:38:22 发布

原创最新推荐文章于 2019-06-04 13:38:22 发布 · 301 阅读

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#LeetCode #Letter Combinations

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本文介绍了一种使用递归算法生成电话号码所有可能的字母组合的方法。通过建立数字到字母的映射表，并利用深度优先搜索策略实现组合生成。

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"].

思路：使用递归算法，查表。

import java.util.ArrayList;
import java.util.List;

public class Solution {
	public List<String> letterCombinations(String digits) {
	    List<String> result = new ArrayList<String>();
	    if(digits == null || digits.length() == 0){
	        return result;
	    }
		String[] map = new String[10];
		map[0] = "";
		map[1] = "";
		map[2] = "abc";
		map[3] = "def";
		map[4] = "ghi";
		map[5] = "jkl";
		map[6] = "mno";
		map[7] = "pqrs";
		map[8] = "tuv";
		map[9] = "wxyz";
		char[] middleTemp = new char[digits.length()];
		dfsGetStr(digits, 0, middleTemp, map, result);
		return result;
	}

	private void dfsGetStr(String digits, int index, char[] middleStr, String[] map, List<String> result) {
		if (index == digits.length()) {
			result.add(new String(middleStr));
			return;
		}
		char strChar = digits.charAt(index);
		for (int i = 0; i < map[strChar - '0'].length(); i++) {
			middleStr[index] = map[strChar - '0'].charAt(i);
			dfsGetStr(digits, index + 1, middleStr, map, result);
		}
	}
}