LeetCode 43 Multiply Strings（高精度乘法）

discription

num1

num2

注意：

solution

code

class Solution
{
public:
string add(string str1, string str2) //高精度加法
{
string str;

int len1 = str1.length();
int len2 = str2.length();
//前面补0，弄成长度相同
if (len1 < len2)
{
for (int i = 1; i <= len2 - len1; i++)
str1 = "0" + str1;
}
else
{
for (int i = 1; i <= len1 - len2; i++)
str2 = "0" + str2;
}
len1 = str1.length();
int cf = 0;
int temp;
for (int i = len1 - 1; i >= 0; i--)
{
temp = str1[i] - '0' + str2[i] - '0' + cf;
cf = temp / 10;
temp %= 10;
str = char(temp + '0') + str;
}
if (cf != 0)
str = char(cf + '0') + str;
return str;
}
string multiply(string str1, string str2)
{
if (str1 == "0" || str2 == "0")
return "0";
string str;
int len1 = str1.length();
int len2 = str2.length();
string tempstr;
for (int i = len2 - 1; i >= 0; i--)
{
tempstr = "";
int temp = str2[i] - '0';
int t = 0;
int cf = 0;
if (temp != 0)
{
for (int j = 1; j <= len2 - 1 - i; j++)
tempstr += "0";
for (int j = len1 - 1; j >= 0; j--)
{
t = (temp * (str1[j] - '0') + cf) % 10;
cf = (temp * (str1[j] - '0') + cf) / 10;
tempstr = char(t + '0') + tempstr;
}
if (cf != 0)
tempstr = char(cf + '0') + tempstr;
}
str = add(str, tempstr);
}
str.erase(0, str.find_first_not_of('0'));
return str;
}
};