Leetcode--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.

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Math String

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思路：
11
*11
-------
11
11
------
121
模拟这个过程，第一层的结果保存到一个vector中，而后的每一层的结果都加到这个vector中，vector的最大长度为num1.size()+num2.size()

class Solution {
public:
string multiply(string num1, string num2) {
if(num1.size()==0||num2.size()==0)
return "";
else if(num1=="0"||num2=="0")
return "0";
string result="";
vector<int> res(num1.size()+num2.size(),0);
for(int i=num2.size()-1;i>=0;i--)
{
int temp=num2[i]-'0';
for(int j=num1.size()-1;j>=0;j--)
{
res[i+j+1]+=temp*(num1[j]-'0');
if(res[i+j+1]>9)
{
res[i+j]+=res[i+j+1]/10;
res[i+j+1]=res[i+j+1]%10;
}
}
}
int k=0;
while(res[k]==0) k++;
for(int l=k;l<res.size();l++)
{
stringstream stream;
stream<<res[l];
string tem="";
stream>>tem;
result+=tem;
}
return result;
}
};