编程算法 - 大整数乘法

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大整数乘法

本文地址: http://blog.csdn.net/caroline_wendy/article/details/29353263

题目:

大整数乘法, 给定两个长度不超过10000的整数, 返回乘法的结果.

char* multi(char* number_a, char* number_b)

代码:

/* * test.cpp * *  Created on: 2014.04.24 *      Author: Spike *//*eclipse cdt, gcc 4.8.1*/#include <iostream>#include <cstring>using namespace std;char* multi(char* number_a, char* number_b) {    int len_a = strlen(number_a); //计算长度    int len_b = strlen(number_b);    int* num_arr = new int[len_a+len_b];    memset(num_arr, 0, sizeof(int)*(len_a+len_b)); //置0    for (int i=len_a-1; i>=0; --i) { //计算每一位        for (int j=len_b-1; j>=0; --j) {        num_arr[i+j+1] += (number_b[j]-'0')*(number_a[i]-'0');        }    }    for (int i=len_a+len_b-1; i>=0; --i) { //进位        if (num_arr[i] >= 10) {        num_arr[i-1] += num_arr[i]/10;        num_arr[i] %= 10;        }    }    char* result = new char[len_a+len_b+1];    for( int i=0; i<(len_a+len_b); ++i){    result[i] = (char)(((int)'0')+num_arr[i]);    }    result[len_a+len_b] = '\0'; //添加结束符    delete[] num_arr;    return result;    //delete[] r;}int main(void){    char* number_a = "10089328947197491751797009791032";    char* number_b = "837190274291741974109721921321451";    std::cout << number_a << " * " << number_b << " = " << std::endl;    char* result = multi(number_a, number_b);    std::cout << result << std::endl;    delete[] result;    return 0;}

输出:

10089328947197491751797009791032 * 837190274291741974109721921321451 = 08446688068723880396297437187783381747295407214602740206809027432

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