[算法题] 大数乘法运算

来源：互联网发布：mac版ps cs6教程编辑：程序博客网时间：2024/05/06 09:58
做算法题时实现的一份大数乘法运算代码。没来得及详细整理，读者可以参考一下。
代码可以在VS2005上直接运行。
#include "stdafx.h"#include <stdio.h>#include <string>#include <iostream>using namespace std;#define OK     0#define ERROR -1/* 函数声明 */void calc1(char* pcStrA, int iLenA, int* piTmp, int num); void accumulate(int iIndex, int *piResult, int iLenResult, int *piTemp, int iLenTemp);char* BignumMultiply(char* pcNumA,int iLenA,char* pcNumB,int iLenB,char* pcResult,int iLenResult); /*===============================================================             调用calc1和accumulate函数计算大数相乘 ===============================================================*/char* BignumMultiply(    char* pcNumA,    int iLenA,    char* pcNumB,    int iLenB,    char* pcResult,    int iLenResult) {     int i     = 0;    int j     = 0;    int num   = 0;    int index = 0;    int *piTmp    = NULL;    int *piResult = NULL;        /* 分配临时结果的存放空间 */     piTmp=(int*)malloc((iLenA+1)*sizeof(int));     piResult=(int*)malloc(iLenResult*sizeof(int));     memset(piTmp, 0, (iLenA+1)*sizeof(int));    memset(piResult, 0, iLenResult*sizeof(int));    for (i = iLenB - 1; i>=0; i--)    {         /* 获取乘数pcNumB中第i位的值 */        num = pcNumB[i] - '0';                 /* 计算被乘数与第i位的乘积,结果保存在piTmp整型数组中 */         calc1(pcNumA,iLenA,piTmp,num);                 /* 将piTmp数组中的值加到piResult数组中 */        index++;        accumulate(index,piResult,iLenResult,piTmp,iLenA+1);     }     //printf("\n%s\n", pcResult);    /* 去掉piResult中第一个非零数字前的零 */    i = 0;    while (piResult[i++]==0);         /* 将整形数组piResult中的值转化成字符串存入pcResult中 */     index = 0;     for (j = i - 1; j < iLenResult; j++, index++)        pcResult[index] = piResult[j] + '0';    if (iLenResult == i - 1)    {        pcResult[1] = '\0';     }    else    {        pcResult[index] = '\0';     }        free(piTmp);     free(piResult);     return pcResult;} /*===============================================================                计算被乘数与乘数的某一位的乘积 ===============================================================*/ void calc1(    char *pcStrA,     int iLenA,     int *piTmp,     int num) {     /* d两个位的乘积结果,remainder余数,carry进位 */     int i         = 0;    int result    = 0;    int remainder = 0;    int carry     = 0;         /* 从被乘数字符串'\0'的前一位算起 */     for (i = iLenA - 1; i >= 0; i--)     {         result = pcStrA[i] - '0';        result *= num;         remainder = (result + carry) % 10;        carry = (result + carry) / 10;         piTmp[i+1] = remainder;     }     if (carry)         piTmp[0] = carry;    else         piTmp[0] = 0; } /*=============================================================== 将被乘数与乘数中一位数字的乘积结果计入res数组中 ==============================================================*/ void accumulate(    int iIndex,    int *piResult,    int iLenResult,    int *piTemp,    int iLenTemp) {     int i = 0;    int j = 0;    int m = 0;    int n = 0;    int remainder = 0;    //余数    static int carry=0;     for (j = iLenTemp - 1, i = 0; j >= 0; j--, i++)     {         m = piTemp[j];         n = piResult[iLenResult-iIndex-i];         if (m + n + carry >= 10)        {             remainder = (m + n + carry) % 10;             carry = 1;        }        else         {             remainder = m + n +carry;             carry = 0;         }        piResult[iLenResult - iIndex - i] = remainder;     } }/***************************************************************************** Prototype    : multiply Description  : 两个任意长度的长整数相乘, 输出结果 Input Param  :                 const std::string strMultiplierA  乘数A                const std::string strMultiplierB  乘数B Output       :                 std::string strRst            乘法结果 Return Value :                 int                       0  正确                                           -1  异常*****************************************************************************/int multiply (const std::string strMultiplierA,const std::string strMultiplierB, std::string &strRst) {    int i = 0;    int j = 0;    int lenA = 0;    int lenB = 0;    int lenResult = 0;    char *pcNumA = NULL;     char *pcNumB = NULL;    char *pcResult = NULL; /* 计算两个字符串的长度,及存储结果所需要的空间 */     lenA = (int)strMultiplierA.length();    lenB = (int)strMultiplierB.length();     if (0 == lenA || 0 == lenB)    {        return ERROR;    }    pcNumA = (char*)strMultiplierA.c_str();    pcNumB = (char*)strMultiplierB.c_str();    lenResult = lenA + lenB + 1; /* 分配并初始化字符串数组 */    pcResult = (char*)malloc(lenResult * sizeof(char));     memset(pcResult, 0, lenResult);    for (i = 0; i < lenResult-1; i++)         *(pcResult + i) = '0'; /* 计算并输出计算结果 */    //printf("The result is: %s",BignumMultiply(pcNumA,lenA,pcNumB,lenB,pcResult,lenResult));    BignumMultiply(pcNumA,lenA,pcNumB,lenB,pcResult,lenResult);    for (i = 0; i < (int)strlen(pcResult); i++)    {        strRst += pcResult[i];    }    //printf("\n%s\n", pcResult);    free(pcResult);    return OK;}int main(void){    string str1 = "111111";    string str2 = "222222";    string str3;    multiply(str1, str2, str3);    cout << str1 << " * " << str2 << " = ";    cout << str3 << endl;    return 0;}
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