43. Multiply Strings

class Solution {
public:
string multiply(string num1, string num2) {
string result="";
int m=num1.size(),n=num2.size();

vector<int> ans(m+n,0);

reverse(num1.begin(),num1.end());
reverse(num2.begin(),num2.end());

for(int i=0;i<m;i++){
for(int j=0;j<n;j++){
ans[i+j]+=(num1[i]-'0')*(num2[j]-'0');
ans[i+j+1]+=ans[i+j]/10;
ans[i+j]%=10;
}
}

int i=m+n-1;
while(i>0 && ans[i]==0) i--;

for(;i>=0;i--) result+=to_string(ans[i]);

return result;
}
};