0043-multiply-strings.cs

publicclassSolution
{
//T: O(m*n) | S: O(m+n)
publicstringMultiply(stringnum1,stringnum2)
{
if(string.Equals(num1,"0")||string.Equals(num2,"0"))
return"0";
varm=num1.Length;
varn=num2.Length;

varresult=newint[m+n];

num1=Reverse(num1);
num2=Reverse(num2);

for(vari1=0;i1<num1.Length;i1++)
{
for(vari2=0;i2<num2.Length;i2++)
{

vardigit=(num1[i1]-'0')*(num2[i2]-'0');
result[i1+i2]+=digit;
result[i1+i2+1]+=(result[i1+i2])/10;
result[i1+i2]=(result[i1+i2])%10;
}
}

Array.Reverse(result);
vari=0;
while(i<result.Length&&result[i]==0)
{
i++;
}

varstr=newStringBuilder();
for(;i<result.Length;i++)
{
//Console.WriteLine(result[i]);
str.Append(result[i]);
}
returnstr.ToString();

}

privatestringReverse(stringstr)
{
vararray=str.ToCharArray();
Array.Reverse(array);
returnnewstring(array);
}
}