Multiply Java Edition by large number

When engaged in ACM encountered large number multiplication problem, on the Internet to find a bit, saw a C + + version of the

http://blog.csdn.net/jianzhibeihang/article/details/4948267

Made a version of Java

Here's the idea.

The number is received as a string, converted to a int[] integer array, and then num1[],num2[] multiplied, the result is saved to result[]

Other notes are noted in the notes

1  Packagecom.gxf.test;2 3 ImportJava.util.Scanner;4 5  Public classbigdatamultiply {6 7      Public Static voidMain (string[] args) {8         Final intN = 100;//multiply by 100-digit maximum9Scanner Scanner =NewScanner (system.in);Ten          One         intNum1[] = Getnum (scanner);//Save the first number 12345 A         intNum2[] = Getnum (scanner);//Save a second number 12345 -          -         intResult[] =New int[2 *N]; the         //The first number 12345 each bit multiplied by the second number 12345 each, the result is put into result[] -         //Note 5 times every digit is saved in result[0] [1] [2] [3] [4] -         //4 multiply each digit by the value in [1] [2] [3] [4] -          for(inti = 0; i < num1.length; i++){ +              for(intj = 0; J < Num2.length; J + +){ -Result[i + j] + = num1[i] *Num2[j]; +             } A}//The resulting results also require rounding and shift processing at         //rounding and Shift handling -          for(inti = 0; I < 2 * N-1; i++){ -Result[i + 1] + = Result[i]/10; -Result[i] = result[i]% 10; -         } -         //Find the result length in         intLength = 2 * N-1; -          while(Result[length] = = 0) tolength--; +         //output Note first output high-top bits are saved in the array -          for(inti = length; I >= 0; i--){ theSystem.out.print (Result[i] + ""); *         } $ scanner.close ();Panax Notoginseng     } -      Public Static int[] Getnum (Scanner Scanner) { the         Final intN = 100; +         intNum[] =New int[N]; A         Chararray_char[]; theString Str_num = ""; +         //Scanner Scanner = new Scanner (system.in);//for receiving input -          $Str_num =Scanner.next (); $Array_char = Str_num.tochararray ();//string 12345 has been converted into a character array -         //converts a character array to an int array -         intLength =array_char.length; the          for(inti = 0; i < array_char.length; i++){ -Num[length-i-1] = array_char[i]-' 0 ';//note here that the saved position is kept high in the array and the lows are saved in the array subscript.Wuyi             //because the back of the calculation is from the lower subscript the             //Num[i] = array_char[i] -         }         Wu         //scanner.close (); -         returnnum; About     } $}

PS: Why here result[] size is 2*n, assuming that two number is 3 digits, such as 565 * 898 can not be greater than 1000 * 1000, and 1000 * 1000 is exactly 2 * 3 = 6 bits

Multiply Java Edition by large number