思路：使用递归
class Solution {
public static Map<Character,char[]> map = new HashMap<>();
{
char[] tmp1 = {};
map.put('1',tmp1);
char[] tmp2={'a','b','c'};
map.put('2',tmp2);
char[] tmp3={'d','e','f'};
map.put('3',tmp3);
char[] tmp4={'g','h','i'};
map.put('4',tmp4);
char[] tmp5={'j','k','l'};
map.put('5',tmp5);
char[] tmp6={'m','n','o'};
map.put('6',tmp6);
char[] tmp7={'p','q','r','s'};
map.put('7',tmp7);
char[] tmp8={'t','u','v'};
map.put('8',tmp8);
char[] tmp9={'w','x','y','z'};
map.put('9',tmp9);
}
public List<String> letterCombinations(String digits) {
List<String> zz = new ArrayList<>();
if(digits.length()==0)
return zz;
addToList(0,digits,zz,"");
return zz;
}
public void addToList(int i,String digits,List<String> zz,String fuck){
if(i==digits.length()){
zz.add(fuck);
return;
}
for(int j=0;j<map.get(digits.charAt(i)).length;j++){
addToList(i+1,digits,zz,fuck+map.get(digits.charAt(i))[j]);
}
}
}
