双十进制字符串

Question

我在java中编写了我自己的大整数类，没有导入，并且需要一种将字符串表示的任意大小数加倍的方法。我现在的代码现在可以运行，但一旦数字变得越来越大，开始需要很长时间。我基本上创建了两个数组：主数组和倒数数组，它们都以相同的方式开始。然后，我运行一个while循环并向上递增主数组并向下递增倒数数组。当倒数数组达到“0”时，我终止循环，结果是一个新数组，新数字的大小加倍。那么当然，我有if语句来检查数组是否需要更改十位数等....这是我的...有什么办法可以使它更高效和快速？

public static String doubleDecimalString (String main) { 
    String countdown = main;  
    String finalBuild = ""; 
    boolean runLoop = true; 

    //if zero is supplied, skip all the nonsense and just return 0 
    //else, loop through and find the true double 

    //was having trobule getting single digits to double correctly so i had to hard code this for now. 
    if (main.equals("0")) { 
     return main; 
    } else if (main.equals("5")) { 
     return "10"; 
    } else if (main.equals("6")) { 
     return "12"; 
    } else if (main.equals("7")) { 
     return "14"; 
    } else if (main.equals("8")) { 
     return "16"; 
    } else if (main.equals("9")) { 
     return "18"; 
    } else { 
     //Array for ORIGINAL NUMBER 
     int[] mainPiece = new int[main.length()+2]; 
     int arrayLength = mainPiece.length; 

     for (int i = 0; i < main.length(); i++) { 
      mainPiece[i+2] = Integer.parseInt(main.substring(i, i+1)); 
     } 
     mainPiece[0] = -1; 
     mainPiece[1] = -1; 

     //Array for COUNTDOWN NUMBER 
     int[] countdownPiece = new int[main.length()+2]; 

     for (int i = 0; i < main.length(); i++) { 
      countdownPiece[i+2] = Integer.parseInt(main.substring(i, i+1)); 
     } 
     countdownPiece[0] = -1; 
     countdownPiece[1] = -1; 

     while ( runLoop) { 

      //Increment and decrement the two arrays 
      mainPiece[arrayLength-1] += 1;  
      countdownPiece[arrayLength-1] -= 1;   

      //UPDATE MAIN ARRAY 
      if ( mainPiece[arrayLength-1] == 10) { 
       for (int x = arrayLength-1; x > 0; x--) { 

        if ((mainPiece[x] == 10) && (mainPiece[x-1] != 9)) { 
         mainPiece[x] = 0; 
         mainPiece[x -1] += 1; 
        } else if ((mainPiece[x] == 10) && (mainPiece[x-1] == 9)) { 
         mainPiece[x] = 0; 
         mainPiece[x -1] += 1;  
         x = arrayLength; 
        } 
        if ((mainPiece[2] == 10)) { 
         mainPiece[1] = 1; 
         mainPiece[2] = 0; 
        } 

       } 
      } // end main array 

      //UPDATE SIDE ARRAY 
      if ( countdownPiece[arrayLength-1] == -1) { 
       for (int x = arrayLength-1; x > 0; x--) { 

        if ((countdownPiece[x] == -1) && (countdownPiece[x-1] > 0) && (x > 1) ) { 
         countdownPiece[x] = 9; 
         countdownPiece[x -1] -= 1; 
        } else if ((countdownPiece[x] == -1) && (countdownPiece[x-1] == 0) && (x > 1)) { 
         countdownPiece[x] = 9; 
         countdownPiece[x -1] -= 1;  
         x = arrayLength; 
        } 

       } 
      } //end side array 


      //tests whether the pieces need to be switched to -1 for scanning 
      for (int x = 0; x < arrayLength - 1; x++) { 
        if ((countdownPiece[x] == -1) && (countdownPiece[x+1] == 0)) { 
         countdownPiece[x+1] = -1; 
        } 
      } 

      //if the side array has reached "0" then the loop will stop and the main array will return the new doubled value 
      if ((countdownPiece[arrayLength-1] == -1) && (countdownPiece[arrayLength-2] == -1)) { 
       break; 
      } 

     } //end while loop 

      //transform array into string 
      finalBuild = "";  
      for (int T = 0; T < arrayLength; T++) { 
       finalBuild += (mainPiece[T] != -1) ? mainPiece[T] : ""; 
      } 
       return finalBuild; 
    }   

} 

Answer 1

如何像这样（它基本上由两个做乘法，占载）：

private String doubleNumber(String number) 
{ 
    int doubleDig = 0; 
    int carry = 0; 

    StringBuilder sb = new StringBuilder(); 
    for (int i = number.length() - 1; i >= 0; --i) 
    { 
     char c = number.charAt(i); 
     int origNum = Character.getNumericValue(c); 
     doubleDig = origNum * 2 + carry; 
     carry = doubleDig/10; 
     doubleDig = doubleDig % 10; 

     sb.append(doubleDig); 
    } 
    if (carry > 0) 
    { 
     sb.append(carry); 
    } 

    return sb.reverse().toString(); 
} 

显然，这只能处理整数。

Answer 2

我会使用StringBuilder或List来建立你的doubled值。

使用随身携带变量来存储运送量并初始化为0

开始在至少显著位，双位数字，并添加进。

然后设置carry到digit/10，那么digit到digit % 10

追加digit到您的制造商或列表。

循环遍历所有数字后，检查carry是否大于0并在需要时追加。

反转StringBuilder或列表并加入，你有你的答案。

public class Doubler { 
    public static void main(String[] args) { 
     System.out.println(doubleDec("9123123123087987342348798234298723948723987234982374928374239847239487.23233099")); 
    } 

    public static String doubleDec(String dec) { 
    StringBuilder builder = new StringBuilder(); 
    int carry = 0; 
    for (int i = dec.length() - 1; i > -1 ; i--) { 
     char charDigit = dec.charAt(i); 
     if (charDigit == '.') { 
     builder.append(charDigit); 
     } else { 
     int digit = Character.getNumericValue(charDigit); 
     if (digit == -1) { 
      throw new IllegalStateException("Invalid character in decimal string."); 
     } 
     digit = digit * 2 + carry; 
     carry = digit/10; 
     digit = digit % 10; 
     builder.append(digit); 
     } 
    } 
    if (carry != 0) { 
     builder.append(carry); 
    } 
    return builder.reverse().toString(); 
    } 
} 

// 18246246246175974684697596468597447897447974469964749856748479694478974.46466198