我正在准备面试问题而不是作业。关于如何复用非常长的整数有一个问题。任何人都可以用C ++提供任何源代码来学习吗？我试图通过学习其他解决方案来改善自己，从而缩小我和他人之间的差距。
非常感谢！
很抱歉，如果您认为这不是提出此类问题的正确位置。
答案 0 :(得分：5)
您可以将GNU Multiple Precision Arithmetic Library用于C ++。
如果你只想要一个简单的方法来乘以大数（整数），那么你就是：
#include<iostream>
#include<string>
#include<sstream>
#define SIZE 700
using namespace std;
class Bignum{
int no[SIZE];
public:
Bignum operator *(Bignum& x){ // overload the * operator
/*
34 x 46
-------
204 // these values are stored in the
136 // two dimensional array mat[][];
-------
1564 // this the value stored in "Bignum ret"
*/
Bignum ret;
int carry=0;
int mat[2*SIZE+1][2*SIZE]={0};
for(int i=SIZE-1;i>=0;i--){
for(int j=SIZE-1;j>=0;j--){
carry += no[i]*x.no[j];
if(carry < 10){
mat[i][j-(SIZE-1-i)]=carry;
carry=0;
}
else{
mat[i][j-(SIZE-1-i)]=carry%10;
carry=carry/10;
}
}
}
for(int i=1;i<SIZE+1;i++){
for(int j=SIZE-1;j>=0;j--){
carry += mat[i][j]+mat[i-1][j];
if(carry < 10){
mat[i][j]=carry;
carry=0;
}
else{
mat[i][j]=carry%10;
carry=carry/10;
}
}
}
for(int i=0;i<SIZE;i++)
ret.no[i]=mat[SIZE][i];
return ret;
}
Bignum (){
for(int i=0;i<SIZE;i++)
no[i]=0;
}
Bignum (string _no){
for(int i=0;i<SIZE;i++)
no[i]=0;
int index=SIZE-1;
for(int i=_no.length()-1;i>=0;i--,index--){
no[index]=_no[i]-'0';
}
}
void print(){
int start=0;
for(int i=0;i<SIZE;i++)
if(no[i]!=0){
start=i;
break; // find the first non zero digit. store the index in start.
}
for(int i=start;i<SIZE;i++) // print the number starting from start till the end of array.
cout<<no[i];
cout<<endl;
return;
}
};
int main(){
Bignum n1("100122354123451234516326245372363523632123458913760187501287519875019671647109857108740138475018937460298374610938765410938457109384571039846");
Bignum n2("92759375839475239085472390845783940752398636109570251809571085701287505712857018570198713984570329867103986475103984765109384675109386713984751098570932847510938247510398475130984571093846571394675137846510874510847513049875610384750183274501978365109387460374651873496710394867103984761098347609138746297561762234873519257610");
Bignum n3 = n1*n2;
n3.print();
return 0;
}
如你所见，它是2个巨大的整数:) ...（最多700位）
答案 1 :(得分：1)
试试这个：
//------------DEVELOPED BY:Ighit F4YSAL-------------
#include<iostream>
#include<string>
#include<sstream>
#define BIG 250 //MAX length input
using namespace std;
int main(){
int DUC[BIG][BIG*2+1]={0},n0[BIG],n1[BIG],i,t,h,carry=0,res;
string _n0,_n1;
while(1){
//-----------------------------------get data------------------------------------------
cout<<"n0=";
cin>>_n0;
cout<<"n1=";
cin>>_n1;
//--------------------string to int[]----------------------------------------
for(i=_n0.length()-1,t=0;i>=0,t<=_n0.length()-1;i--,t++){
n0[i]=_n0[t]-'0';
}
i=0;
for(i=_n1.length()-1,t=0;i>=0,t<=_n1.length()-1;i--,t++){
n1[i]=_n1[t]-'0';
}
i=0;t=0;
//--------------------------produce lines of multiplication----------------
for(i=0;i<=_n1.length()-1;i++){
for(t=0;t<=_n0.length()-1;t++){
res=((n1[i]*n0[t])+carry);
carry=(res/10);
DUC[i][t+i]=res%10;
}
DUC[i][t+i]=carry;
carry=0;
}
i=0;t=0;res=0;carry=0;
//-----------------------------add the lines-------------------------------
for(i=0;i<=_n0.length()*2-1;i++){
for(t=0;t<=_n1.length()-1;t++){
DUC[BIG-1][i]+=DUC[t][i];
//cout<<DUC[t][i]<<"-";
}
res=((DUC[BIG-1][i])+carry);
carry=res/10;
DUC[BIG-1][i]=res%10;
//cout<<" ="<<DUC[BIG-1][i]<<endl;
}
i=0;t=0;
//------------------------print the result------------------------------------
cout<<"n1*n0=";
for(i=_n0.length()*2-1;i>=0;i--){
if((DUC[BIG-1][i]==0) and (t==0)){}else{cout<<DUC[BIG-1][i];t++;}
//cout<<DUC[BIG-1][i];
}
//-------------------------clear all-------------------------------------
for(i=0;i<=BIG-1;i++){
for(t=0;t<=BIG*2;t++){
DUC[i][t]=0;
}
n0[i]=0;n1[i]=0;
}
//--------------------------do it again-------------------------------------
cout<<"\n------------------------------------------------\n\n";
}
return 0;
}
答案 2 :(得分：0)
这个解决方案非常适用于非常大的数字但对于非常大的数字的因子计算不是那么有效。希望它会帮助别人。
#include <iostream>
#include <string>
using namespace std;
string addition(string a, string b) {
string ans = "";
int i, j, temp = 0;
i = a.length() - 1;
j = b.length() - 1;
while (i >= 0 || j >= 0) {
if (i >= 0 && a[i])
temp += a[i] - '0';
if (j >= 0 && b[j])
temp += b[j] - '0';
int t = (temp % 10);
char c = t + '0';
ans = ans + c;
temp = temp / 10;
i--;
j--;
}
while (temp > 0) {
int t = (temp % 10);
char c = t + '0';
ans = ans + c;
temp = temp / 10;
}
string fnal = "";
for (int i = ans.length() - 1;i >= 0;i--) {
fnal = fnal + ans[i];
}
return fnal;
}
string multiplication(string a, string b) {
string a1, b1 = "0";
int i, j, temp = 0, zero = 0;
i = a.length() - 1;
int m1, m2;
while (i >= 0) {
a1 = "";
m1 = a[i] - '0';
j = b.length() - 1;
while (j >= 0) {
m2 = b[j] - '0';
temp = temp + m1*m2;
int t = temp % 10;
char c = t + '0';
a1 = a1 + c;
temp = temp / 10;
j--;
}
while (temp > 0) {
int t = (temp % 10);
char c = t + '0';
a1 = a1 + c;
temp = temp / 10;
}
string fnal = "";
// reverse string
for (int i = a1.length() - 1;i >= 0;i--) {
fnal = fnal + a1[i];
}
a1 = fnal;
//add zero
for (int p = 0;p < zero;p++)
a1 = a1 + '0';
b1 = addition(a1, b1);
i--;
zero++;
}
return b1;
}
// upto 50 is ok
int factorial(int n) {
string a = "1";
for (int i = 2;i <= n;i++) {
string b = to_string(i);
a = multiplication(a, b);
}
cout << a << endl;
return a.length();
}
int main() {
freopen("in.txt", "r", stdin);
freopen("out.txt", "w", stdout);
int n;
cin >> n;
//cout << factorial(n) << endl;
string a, b;
a = "1281264836465376528195645386412541764536452813416724654125432754276451246124362456354236454857858653";
b = "3767523857619651386274519192362375426426534237624548235729562582916259723586347852943763548355248625";
//addition(a, b);
cout << multiplication(a, b);
return 0;
}