大数相乘（java）

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package com.java.mytry;

import java.util.Scanner;

import javafx.collections.ListChangeListener.Change;

/**
* 大数相乘
* @author Dong
*
*/
public class Mulyiplication_of_large_Number {

   public static void main(String[] args) {
       Scanner in = new Scanner(System.in);
       String str1 = in.next();
       String str2 = in.next();

       int len1 = str1.length();
       int len2 = str2.length();

       char[] s1 = str1.toCharArray();
       char[] s2 = str2.toCharArray();

       Change(len1,s1);
       Change(len2,s2);

       System.out.println( str1);
       System.out.println(" * ");
       System.out.println( str2);
       System.out.println( " = ");


       Mulyiplication(s1,len1,s2,len2);

   }

   /**
   * 逐位相乘
   * @param s1 乘数
   * @param len1 乘数长度
   * @param s2 被乘数
   * @param len2 被乘数长度
   */
   private static void Mulyiplication(char[] s1, int len1, char[] s2, int len2) {
       //两位乘积位数
       int size = len1 +len2 +3;
       int []result = new int[size];

       for(int i = 0;i<size;i++){
           result[i] = 0;
       }

       //逐位相乘
       for(int i = 0;i<len2;i++){
           for(int j=0;j<len1;j++){
               result[i+j] += (int)(s2[i]-'0') * (int)(s1[j]-'0') ;
           }
       }

       for(int i = 0;i<size;i++){
           int carry = result[i]/10;
           result[i] = result[i]%10;

           if(carry>0)
               result[i+1] += carry;
       }
       int i;
       for( i = size-1;i>=0;i--){
           if(result[i] > 0)
               break;
       }

       for(int j = 0;j<=i;j++){
           System.out.print(result[i-j]);
       }


   }

   /**
   * 字符数组倒置
   * @param len 数组长度
   * @param s 需要倒置的数组
   */
   private static void Change(int len, char[] s) {
       //高低位对调
       for(int i = 0;i<len/2;i++){
           s[i] += s[len - 1 - i];
           s[len - 1 - i] = (char)(s[i] - s[len - 1 - i]);
           s[i] = (char)(s[i] - s[len - 1 - i]);


       }
   }

}

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