C/C++编程题之大数相乘

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大数相乘算法：第一位与第一位相乘如果大于10，则对10取于，余数保留，再对除10，除数进位。循环对每一位进行相同的操作则最后的结果即为所求。

#include <string.h>#include <map>using std::map;void InverseStr(char* str){if(str == NULL)return;int leA = (int)strlen(str);char ch;for(int i = 0; i < len/2;i++){ch = str[i];str[i] = str[len - 1 - i];str[lenA - 1 - i] = ch;}}int multiply (const std::string strMultiplierA,const std::string strMultiplierB, std::string &strRst) {    /* 在这里实现功能 */    char *strA = (char*)strMultiplierA.c_str();char *strB = (char*)strMultiplierB.c_str();if(strA == NULL || strB == NULL)return -1;int lenA = (int)strlen(strA);int lenB = (int)strlen(strB);if(lenA == 0 || lenB == 0)return -1;char *rst = (char*)malloc(lenA + lenB +1);if(*strA == '0' || *strB == '0'){strRst = "0";free(rst);return 0;}InverseStr(strA);//strA进行倒置InverseStr(strB);map<int,int> m_mapA;map<int,int> m_mapB;map<int,int> m_mapC;int cnt = 0;while(*(strA) != '\0')//将strA放入map中{m_mapA[cnt++] = *strA - '0';strA++;}cnt = 0;while(*strB != '\0'){m_mapB[cnt++] = *strB - '0';strB++;}cnt = 0;map<int,int>::iterator iteA = m_mapA.begin();map<int,int>::iterator iteB = m_mapB.begin();for(;iteB != m_mapB.end();iteB++)//主程序大数相乘的处理，最后放入m_mapC中{for(iteA = m_mapA.begin();iteA != m_mapA.end();iteA++){m_mapC[iteB->first + iteA->first] += (iteB->second * iteA->second)%10;if(m_mapC[iteB->first + iteA->first] >= 10){m_mapC[iteB->first + iteA->first + 1] += m_mapC[iteB->first + iteA->first]/10;m_mapC[iteB->first + iteA->first] %= 10;}m_mapC[iteB->first + iteA->first + 1] += (iteB->second * iteA->second)/10;if(m_mapC[iteB->first + iteA->first + 1] >= 10){m_mapC[iteB->first + iteA->first + 2] += m_mapC[iteB->first + iteA->first + 1]/10;m_mapC[iteB->first + iteA->first + 1] %= 10;}}}map<int,int>::iterator iteC = m_mapC.begin();for(;iteC != m_mapC.end();iteC++){rst[iteC->first] = iteC->second + '0';cnt = iteC->first;}rst[++cnt] = '\0';InverseStr(rst);if(*rst == '0'){strRst = rst + 1;free(rst);    return 0;}strRst = rst;free(rst);    return 0;}

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