043 - Multiply Strings

Given two numbers represented as strings, return multiplication of the numbers as a string.

Note: The numbers can be arbitrarily large and are non-negative.

static void turnaround(char *str){int str_length = strlen(str);char temp;int i;for(i = 0;i < str_length / 2;i ++){temp = str[i];str[i] = str[str_length - 1 - i];str[str_length - 1 - i] = temp;}}char *multiply(char *multiplier, char *multiplicand){int num1_length = strlen(multiplier);int num2_length = strlen(multiplicand);char *num1 = (char *)malloc(sizeof(char) * (num1_length + 1));char *num2 = (char *)malloc(sizeof(char) * (num2_length + 1));char *result = (char *)calloc(sizeof(char), num1_length + num2_length + 1);memcpy(num1, multiplier, num1_length + 1);memcpy(num2, multiplicand, num2_length + 1);turnaround(num1);turnaround(num2);int i,j,carry = 0,tem_num1,tem_num2;for(i = 0;i < num2_length;i ++){for(j = 0;j < num1_length;j ++){tem_num1 = num1[j] - '0';tem_num2 = num2[i] - '0';result[j + i] += (tem_num2 * tem_num1) % 10 + carry;carry = tem_num2 * tem_num1 > 9? tem_num2 * tem_num1 / 10 : 0;while(result[j + i] > 9){//tem_num1 * tem_num2 <= 9 && tem_num1 * tem_num2 + carry > 9carry += 1;result[j + i] -= 10;}}int e = 0;while(carry){//i == num2_lengthresult[j + i + e] += carry;if(result[j + i + e] > 9){result[j + i + e] -= 10;carry = 1;}elsecarry = 0;e += 1;}}//change the result from Hexadecimal to stringfor(i = 0;i < num1_length + num2_length;i ++)result[i] += '0';//clear the end '0'char *p2mymulend = result + strlen(result) - 1;while(*p2mymulend == '0'){*p2mymulend-- = 0x00;if(p2mymulend - result == 0)break;}if(num1) free(num1);if(num2) free(num2);turnaround(result);return result;}