使用数组计算大量乘积? [英] Calculating products of large numbers using arrays?
问题描述
我有一个项目(用于学校),我绝对不能使用任何外部库,因此不能使用任何大数库,我需要得到2个(非常大数)的乘积.所以我想我会为此写我自己的代码,但是我似乎无法获得传递一位数的乘法.
I have a project (for school) and I absolutely cant use any external libraries hence cannot use any big numbers library and I need to get the product of 2 (very) large numbers. So I thought I'll actually write my own code for it but I cant seem to get pass single digit multiplications.
到目前为止,我的工作方式是我有一个字符'a'数组.病态将其每个数字与另一个数字相乘(因为任何乘法都不能超过81,即9 * 9).但是我似乎无法弄清楚如何将两个数组彼此相乘.
How I've done it so far is I have an array of chars 'a'. And Ill multiply each of its digits with the other number (since no multiplication can go beyond 81 ie, 9*9). But I cant seem to figure out how Ill multiply two arrays with each other.
如
int a[] = {1,2,3};
int b[] = {4,5,6};
int r[200]; // To store result of 123x456. After processing should have value 56088
到目前为止,这里有我的代码...
Heres my code so far...
#include <iostream>
using namespace std;
void reverseArray(int array[], int n)
{
int t;
for(int i=0;i<n/2;i++)
{
t = array[i];
array[i] = array[n-i-1];
array[n-i-1] = t;
}
}
int main()
{
int A[] = {1,2,6,6,7,7,8,8,8,8,8,8,8,8,8,8};
int s = sizeof(A)/sizeof(int);
int n = s-1;
int R[50];
int x = 2;
int rem = 0;
for(int i=0; i<s; i++)
{
R[i] = (A[n-i] * x) % 10;
R[i] += (rem != 0) ? rem:0;
rem = (A[n-i] * x) / 10;
}
reverseArray(R, s);
for(int i=0; i<s; i++) cout<<R[i]; // Gives 2533557777777776
}
I also found a similar program here which calculates factorials of very large numbers. But I cant seem to understand the code enough to change it to my needs.
很抱歉,这个问题有点粗略.
Sorry if the question is a little sketchy.
谢谢.
推荐答案
我已经用Java完成了,在这里我将数字N1和N2进行了处理,并创建了一个大小为1000的数组.这,N1 = 12,N2 = 1234.对于N1 = 12,temp = N1%10 = 2,现在将此数字从右到左与数字N2相乘,并将结果存储到从i = 0开始的数组中,类似于N1的其余数字.数组将存储结果,但顺序相反.看看这个链接. http://ideone.com/UbG9dW#view_edit_box
I have done in java, Here I am taking to numbers N1 and N2, And I have create an array of size 1000. Lets take an example How to solve this, N1=12, N2=1234. For N1=12, temp=N1%10=2, Now Multiply this digit with digit N2 from right to Left and store the result into array starting from i=0, similarly for rest digit of N1. The array will store the result but in reverse order. Have a looking on this link. http://ideone.com/UbG9dW#view_edit_box
//Product of two very large number
import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;
class Solution {
public static void main(String[] args) {
Scanner scan=new Scanner(System.in);
int N1=scan.nextInt();
int N2=scan.nextInt();
//int N=scan.nextInt();
int [] array=new int[1000];
Arrays.fill(array,0);
int size=multiply(N1,N2,array);
for(int i=size-1;i>=0;i--){
System.out.print(array[i]);
}
}
public static int multiply(int N1, int N2, int [] result){
int a=N1;
int b=N2;
int count=0, carry=0;
int i=0;
int max=0;
if(a==0||b==0)
return 1;
while(a>0){
int temp1=a%10;
a=a/10;
i=0;
while(b>0){
int temp2=b%10;
b=b/10;
int product=result[count+i]+temp1*temp2+carry;
result[count+i]=product%10;
carry=product/10;
i++;
//System.out.println("ii="+i);
}
while(carry>0){
result[count+i]=carry%10;
carry=carry/10;
i++;
//System.out.println("iiii="+i);
}
count++;
b=N2;
}
//System.out.println("i="+i);
return i+count-1;
}
}
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