Leetcode #17 Letter Combinations of a Phone Number Z9键盘字母组合解题小节

1 题目理解

此道题目基于我们前几年用的，或许还有这几年用的九宫格输入法。九宫格上的每个数字对应着不同的字母，现在说，如果给定你一个数字，问你可以对应到多少种的字母组合？

这道题的解题方式，就是直接递归搜索就好，尝试每种可能。

这道题我觉得考点在于自己程序的书写，如何有效率的保存和组合这些可能的字符。

2 原题

Letter Combinations of a Phone Number

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”].

3 AC解

public class Solution {
//我用来加快检索速度的方式，形成字典final static char[][] map = new char[][]{{},{},{'a','b','c'},{'d','e','f'},{'g','h','i'},{'j','k','l'},{'m','n','o'},{'p','q','r','s'},{'t','u','v'},{'w','x','y','z'}};  List<String> result;char[] chars;public void dfs(String tmp,int index){if(index==chars.length){result.add(tmp);return ;}else{for(int j=0;j<map[chars[index]].length;j++){dfs(tmp+map[chars[index]][j],index+1);}}}public List<String> letterCombinations(String digits) {result=new ArrayList<String>();chars=digits.toCharArray();if(chars.length==0)return result;for(int j=0;j<chars.length;j++){chars[j]-='0';}dfs("",0);return result;}
}

Leetcode #17 Letter Combinations of a Phone Number Z9键盘字母组合解题小节

1 题目理解

此道题目基于我们前几年用的，或许还有这几年用的九宫格输入法。九宫格上的每个数字对应着不同的字母，现在说，如果给定你一个数字，问你可以对应到多少种的字母组合？

这道题的解题方式，就是直接递归搜索就好，尝试每种可能。

这道题我觉得考点在于自己程序的书写，如何有效率的保存和组合这些可能的字符。

2 原题

Letter Combinations of a Phone Number

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”].

3 AC解

public class Solution {
//我用来加快检索速度的方式，形成字典final static char[][] map = new char[][]{{},{},{'a','b','c'},{'d','e','f'},{'g','h','i'},{'j','k','l'},{'m','n','o'},{'p','q','r','s'},{'t','u','v'},{'w','x','y','z'}};  List<String> result;char[] chars;public void dfs(String tmp,int index){if(index==chars.length){result.add(tmp);return ;}else{for(int j=0;j<map[chars[index]].length;j++){dfs(tmp+map[chars[index]][j],index+1);}}}public List<String> letterCombinations(String digits) {result=new ArrayList<String>();chars=digits.toCharArray();if(chars.length==0)return result;for(int j=0;j<chars.length;j++){chars[j]-='0';}dfs("",0);return result;}
}