大数乘法

算法描述：使用int[] input1和int[] input2存储被乘数和乘数，使用int[input1.length+input2.length] result存储计算结果，具体计算过程可以结合代码和示意图理解

import java.util.Scanner;

public class Multiply {

    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        String input1=sc.next();
        String input2=sc.next();

        if (input1.charAt(0)=='-'){
            input1=input1.substring(1);
        }
        if (input2.charAt(0)=='-'){
            input2=input2.substring(1);
        }
        String result=multiply(input1,input2);
        System.out.println("result:"+result);
    }

    public static String multiply(String num1, String num2) {
        //把字符串转成char数组
        char[] chars1 = num1.toCharArray();
        char[] chars2 = num2.toCharArray();
        
        //声明存放结果和两个乘积的容器
        int[] result = new int[chars1.length + chars2.length];
        int[] n1= new int[chars1.length];
        int[] n2= new int[chars2.length];
        
        //把char转换成int数组。
        for (int i =0; i < chars1.length; i++){
            n1[i] = chars1[i] - '0';
        }
        
        for (int j =0; j < chars2.length; j++){
            n2[j] = chars2[j] - '0';
        }
        
        //逐个相乘
        for (int i = 0; i < chars1.length; i++){
            for (int j = 0; j < chars2.length; j++) {
                result[i+j] += n1[i]  *  n2[j];
            }
        }
        
        //从后往前满十进位
        for (int i = result.length -1; i > 0; i--) {
            result[i-1] += result[i] / 10;
            result[i] = result[i] % 10;
        }
        
        //转成string并返回
        String resultStr = "";
        for (int i = 0; i < result.length - 1; i++) {
            resultStr +=result[i];
        }
        return resultStr;
    }
}