Difference of two large numbers http://www.geeksforgeeks.org/difference-of-two-large-numbers/

ver1.c

// C++ program to find difference of two large numbers.
#include<bits/stdc++.h>
using namespace std;
 
// Returns true if str1 is smaller than str2.
bool isSmaller(string str1, string str2)
{
    // Calculate lengths of both string
    int n1 = str1.length(), n2 = str2.length();
 
    if (n1 < n2)
       return true;
    if (n2 < n1)
       return false;
 
    for (int i=0; i<n1; i++)
       if (str1[i] < str2[i])
          return true;
       else if (str1[i] > str2[i])
          return false;
 
    return false;
}
 
// Function for find difference of larger numbers
string findDiff(string str1, string str2)
{
    // Before proceeding further, make sure str1
    // is not smaller
    if (isSmaller(str1, str2))
        swap(str1, str2);
 
    // Take an empty string for storing result
    string str = "";
 
    // Calculate length of both string
    int n1 = str1.length(), n2 = str2.length();
 
    // Reverse both of strings
    reverse(str1.begin(), str1.end());
    reverse(str2.begin(), str2.end());
 
    int carry = 0;
 
    // Run loop till small string length
    // and subtract digit of str1 to str2
    for (int i=0; i<n2; i++)
    {
        // Do school mathematics, compute difference of
        // current digits
        int sub = ((str1[i]-'0')-(str2[i]-'0')-carry);
 
        // If subtraction is less then zero
        // we add then we add 10 into sub and
        // take carry as 1 for calculating next step
        if (sub < 0)
        {
            sub = sub + 10;
            carry = 1;
        }
        else
            carry = 0;
 
        str.push_back(sub + '0');
    }
 
    // subtract remaining digits of larger number
    for (int i=n2; i<n1; i++)
    {
        int sub = ((str1[i]-'0') - carry);
        carry = 0;
        str.push_back(sub + '0');
    }
 
    // reverse resultant string
    reverse(str.begin(), str.end());
 
    return str;
}
 
// Driver code
int main()
{
    string str1 = "12";
    string str2 = "198111";
    cout << findDiff(str1, str2);
    return 0;
}

ver2.c

// C++ program to find difference of two large numbers.
#include<bits/stdc++.h>
using namespace std;
 
// Returns true if str1 is smaller than str2,
// else false.
bool isSmaller(string str1, string str2)
{
    // Calculate lengths of both string
    int n1 = str1.length(), n2 = str2.length();
 
    if (n1 < n2)
        return true;
    if (n2 > n1)
        return false;
 
    for (int i=0; i<n1; i++)
    {
        if (str1[i] < str2[i])
            return true;
        else if (str1[i] > str2[i])
            return false;
    }
    return false;
}
 
// Function for finding difference of larger numbers
string findDiff(string str1, string str2)
{
    // Before proceeding further, make sure str1
    // is not smaller
    if (isSmaller(str1, str2))
        swap(str1, str2);
 
    // Take an empty string for storing result
    string str = "";
 
    // Calculate lengths of both string
    int n1 = str1.length(), n2 = str2.length();
    int diff = n1 - n2;
 
    // Initially take carry zero
    int carry = 0;
 
    // Traverse from end of both strings
    for (int i=n2-1; i>=0; i--)
    {
        // Do school mathematics, compute difference of
        // current digits and carry
        int sub = ((str1[i+diff]-'0') -
                   (str2[i]-'0') -
                   carry);
        if (sub < 0)
        {
            sub = sub+10;
            carry = 1;
        }
        else
            carry = 0;
 
        str.push_back(sub + '0');
    }
 
    // subtract remaining digits of str1[]
    for (int i=n1-n2-1; i>=0; i--)
    {
        if (str1[i]=='0' && carry)
        {
            str.push_back('9');
            continue;
        }
        int sub = ((str1[i]-'0') - carry);
        if (i>0 || sub>0) // remove preceding 0's
            str.push_back(sub+'0');
        carry = 0;
 
    }
 
    // reverse resultant string
    reverse(str.begin(), str.end());
 
    return str;
}
 
// Driver code
int main()
{
    string str1 = "88";
    string str2 = "1079";
    cout << findDiff(str1, str2);
    return 0;
}

Would you be able to find difference of two lists
In python.
Example listA= [1,5,9]
ListB=[1,2,9]
Answer= [3,0]

Not using any built in methods. And the list represents the precision integers