大数相乘(1)

题目：两个大数相乘。

 

大数相乘(2)见此。

 

方法1：将两个大数分别用数组存储，模拟乘法运算，将其中一个数组的每一位分别与令一个大数相乘，结果相加。
代码见后面代码部分的string multiply1(bignumber &bignumber2)。

方法2：同样是上面的思路，不同的是存储过程直接用一个二维数组来存取每一位相乘的结果，然后处理相加的过程。
代码见后面代码部分的string multiply2(bignumber &bignumber2)。

 

#include <iostream>#include <string>#include <cstring>using namespace std;class bignumber{private:string bigno;bool checkout;bignumber();bool checknumber(){for(int count = 0; count < bigno.length(); ++count){if(!isdigit(bigno[count])){return false;}}return true;}public:explicit bignumber(const char tocopy[]){bigno = tocopy;checkout = checknumber();}explicit bignumber(const bignumber &tocopy){bigno = tocopy.bigno;checkout = checknumber();}string showvalue(){return bigno;}bool showcheck(){return checkout;}string multiply1(bignumber &bignumber2){if(!(checkout && bignumber2.showcheck())){cout<<"Values are not all positive numbers."<<endl;return "";}int len1 = bigno.length();int len2 = bignumber2.showvalue().length();int *no1 = new int[len1];memset(no1, 0, len1 * sizeof(int));int *no2 = new int[len2];memset(no2, 0, len2 * sizeof(int));int count = 0;for(count = len1; count > 0; --count){no1[count - 1] = (int)(bigno[count - 1]) - 48;}for(count = len2; count > 0; --count){no2[count - 1] = (int)(bignumber2.showvalue()[count - 1]) - 48;}int *convertpointer = new int[len1 + len2];memset(convertpointer, 0, (len1 + len2) * sizeof(int));for(count = len2; count > 0; --count){for(int countrow = len1; countrow > 0; --countrow){convertpointer[countrow + count - 1] += no1[countrow - 1] * no2[count - 1];}}for(count = len1 + len2; count > 0; --count){if(convertpointer[count - 1] > 9){convertpointer[count - 2] += convertpointer[count - 1] / 10;convertpointer[count - 1] = convertpointer[count - 1] % 10;}}char *resultchar = new char[len1 + len2];bool checkresultzero = false;int countresultzero = 0;for(count = 0; count < len1 + len2; ++count){if(!checkresultzero){if(convertpointer[count] != 0){checkresultzero = true;resultchar[countresultzero++] = convertpointer[count] + '0';}}else{resultchar[countresultzero++] = convertpointer[count] + '0';}}resultchar[countresultzero] = '\0';string result = resultchar;delete[] no1;delete[] no2;delete[] convertpointer;delete[] resultchar;return result;}string multiply2(bignumber &bignumber2){if(!(checkout && bignumber2.showcheck())){cout<<"Values are not all positive numbers."<<endl;return "";}int len1 = bigno.length();int len2 = bignumber2.showvalue().length();int **convertcolumn = new int*[len2 + 1];int countcolumn = 0;int countrow = 0;for(countcolumn = 0; countcolumn < len1 + 1; ++countcolumn){convertcolumn[countcolumn] = new int[len1 + len2 + 1];memset(convertcolumn[countcolumn], 0, sizeof(int) * (len1 + len2 + 1));}for(countcolumn = len2 + 1; countcolumn < len1 + len2 + 1; ++countcolumn){convertcolumn[0][countcolumn] = (int)(bigno[countcolumn - len2 - 1]) - 48;}for(countrow = 1; countrow < len2 + 1; ++countrow){convertcolumn[countrow][0] = (int)(bignumber2.showvalue()[countrow - 1]) - 48;}for(countrow = len2; countrow > 0; --countrow){for(countcolumn = len1; countcolumn > 0; --countcolumn){convertcolumn[countrow][len2 + 1 - countrow + countcolumn] = convertcolumn[0][countcolumn + len2] * convertcolumn[len2 + 1 - countrow][0];}}int *convertpointer = new int[len1 + len2];memset(convertpointer, 0, sizeof(int) * (len1 + len2));int count = 0;for(count = len1 + len2; count > 0; --count){for(countrow = 1; countrow < len2 + 1; ++countrow){convertpointer[count - 1] += convertcolumn[countrow][count];}if(convertpointer[count - 1] > 9){convertpointer[count - 2] += convertpointer[count - 1] / 10;convertpointer[count - 1] = convertpointer[count - 1] % 10;}}char *resultchar = new char[len1 + len2];bool checkresultzero = false;int countresultzero = 0;for(count = 0; count < len1 + len2; ++count){if(!checkresultzero){if(convertpointer[count] != 0){checkresultzero = true;resultchar[countresultzero++] = convertpointer[count] + '0';}}else{resultchar[countresultzero++] = convertpointer[count] + '0';}}resultchar[countresultzero] = '\0';string result = resultchar;for(countcolumn = 0; countcolumn < len1 + 1; ++countcolumn){delete[] convertcolumn[countcolumn];}delete[] convertcolumn;delete[] convertpointer;delete[] resultchar;return result;}};int main(){bignumber aaa("11234567890");bignumber bbb("00123456788");cout<<aaa.showvalue()<<endl<<bbb.showvalue()<<endl;cout<<aaa.multiply1(bbb)<<endl;cout<<aaa.multiply2(bbb)<<endl;return 0;}