43. Multiply Strings
Given two non-negative integers num1
and num2
represented as strings, return the product of num1
and num2
.
Note:
- The length of both
num1
andnum2
is < 110. - Both
num1
andnum2
contains only digits0-9
. - Both
num1
andnum2
does not contain any leading zero. - You must not use any built-in BigInteger library or convert the inputs to integer directly
常规计算,一个被乘数,一个乘数
class Solution { public: string multiply(string num1, string num2) { string sum(num1.size() + num2.size(), '0'); //积的长度初始化为两个数的长度之和 for (int i = num1.size() - 1; 0 <= i; --i) { int carry = 0; for (int j = num2.size() - 1; 0 <= j; --j) { int tmp = (sum[i + j + 1] - '0') + (num1[i] - '0') * (num2[j] - '0') + carry; sum[i + j + 1] = tmp % 10 + '0'; carry = tmp / 10; //进位值计算 } sum[i] += carry; //进位*************注意此处进位进到了被乘数上边 } size_t startpos = sum.find_first_not_of("0"); //找到不是零的开头,即积的有效位的开始。 if (string::npos != startpos) { //npos是一个常数,用来表示不存在的位置, return sum.substr(startpos); //截取有效位 } return "0"; } };