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letterCombinations.java
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31 lines (31 loc) · 1.2 KB
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import java.util.*;
public class letterCombinations {
String[] phone = {"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
public static void main(String[] args){
letterCombinations obj = new letterCombinations();
String digits = "23";
System.out.println(obj.letterCombinations(digits));
}
private List<String> letterCombinations(String digits){
List<String> res = new ArrayList<>();
//以数字，字母为KEY的hashmap其实都可以用个array来代替
//String[] phone = {"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
dfs(0,digits, res,"");
return res;
}
private void dfs(int level, String digits, List<String> res, String path){
if (level == digits.length()){
res.add(path);
return;
}
String cur = phone [(int) digits.charAt(level)-'0'];
System.out.println(cur);
for(char c : cur.toCharArray()){
/* 注意这里！
不能 path += c; dfs(level+1, digits, phone, res,path);
看来要系统学习一下call by reference/call by value
* */
dfs(level+1, digits, res,path+c);
}
}
}