打印從電話號碼的數字所有可能的單詞

Question

我的問題是，有多少個單詞可能用七個數字代替，每個數字代表n個字母？當我們按下2,3,4-打字時可形成一個文本可能的話是（按字母順序）：

如果輸入數目是234， ADG ADH ADI AEG AEH AEI AFG AFH AFI BDG BDH BDI BEG BEH貝BFG BFH BFI CDG CDH CDI CEG CEH CEI CFG CFH CFI

Answer 1

//調用此

List<String> perms = permutation("", "abc"); 
    // instead of "abc write your 7 digit number 

      String[] array = new String[perms.size()]; 
      for (int i = 0; i < perms.size(); i++) { 
       array[i] = perms.get(i); 
      } 

      int x = array.length; 

      for (final String anArray : array) { 
       System.out.println(anArray); 
      } 

//方法爲它

private static List<String> permutation(String prefix, String str) { 
     List<String> permutations = new ArrayList<>(); 
     int n = str.length(); 
     if (n == 0) { 
      permutations.add(prefix); 
     } else { 
      for (int i = 0; i < n; i++) { 
       permutations.addAll(permutation(prefix + str.charAt(i), str.substring(i + 1, n) + str.substring(0, i))); 
      } 
     } 
     return permutations; 
    } 

Answer 2

遞歸溶液：

void printAllWordsFromPhoneNumber(string phonenumber) 
{ 
    printAllWordsFromPrefixAndPhoneNumber("", phonenumber); 
} 

string getLettersForNumber(char digit) 
{ 
    string [] table = {"", "", "ABC", "DEF", "GHI", "JKL", "MNO", "PQRS", "TUV", "WXYZ"}; 
    bool valid = ((digit >= '0') && (digit <= '9')); 
    return valid ? table[digit-'0'] : ""; 
} 

void printAllWordsFromPrefixAndPhoneNumber(string prefix, string remaining) 
{ 
    if ((remaining == null) || (remaining.length()==0)) 
    { 
     System.out.println(prefix); 
    } 
    else 
    { 
     string chars_in_digit = getLettersForNumber(remaining.charAt(0)); 

     for (int i = 0; i < chars_in_digit.length(); i++) 
     { 
      string newprefix = prefix + chars_in_digit.charAt(i); 
      string newremaining = remaining.substr(1); 
      printAllWordsFromPrefixAndPhoneNumber(newprefix, newremaining); 
     } 

     // special case for "0" and "1" since neither has any letters associated with them. 
     if (chars_in_digit.length() == 0) 
     { 
      printAllWordsFromPrefixAndPhoneNumber(prefix, remaining.substr(1)); 
     } 

    } 
}