Difference of two large numbers - GeeksforGeeks

18 Jun, 2021
Given two numbers as strings. The numbers may be very large (may not fit in long long int), the task is to find the difference between these two numbers.
Examples:  
Input : str1 = "11443333311111111100", 
        str2 =     "1144422222221111"
Output : 11442188888888889989

Input :str1 = "122387876566565674",
       str2 =     "31435454654554"
Output : 122356441111911120
This is simply based on school mathematics. We traverse both strings from the end, one by one subtract digits. 
Reverse both strings.Keep subtracting digits one by one from 0’th index (in reversed strings) to the end of a smaller string, append the diff if it’s positive to end of the result. If difference(diff) is negative then add 10 and keep track of carry as 1 if it’s positive then carry is 0.Finally, reverse the result. 
Reverse both strings.
Keep subtracting digits one by one from 0’th index (in reversed strings) to the end of a smaller string, append the diff if it’s positive to end of the result. If difference(diff) is negative then add 10 and keep track of carry as 1 if it’s positive then carry is 0.
Finally, reverse the result. 
Below is the implementation of the above idea: 
C++
Java
Python3
C#
PHP
Javascript
// 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 numbersstring 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);         // if the sub value is -ve, then make it positive        if (sub < 0) {            sub = sub + 10;            carry = 1;        }        else            carry = 0;         str.push_back(sub + '0');    }     // reverse resultant string    reverse(str.begin(), str.end());     return str;} // Driver codeint main(){    string str1 = "978";    string str2 = "12977";     // Function call    cout << findDiff(str1, str2) << endl;     string s1 = "100";    string s2 = "1000000";       // Function call    cout << findDiff(s1, s2);     return 0;}
// Java program to find difference of two large numbers.import java.util.*; class GFG {     // Returns true if str1 is smaller than str2.    static boolean 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.charAt(i) < str2.charAt(i))                return true;            else if (str1.charAt(i) > str2.charAt(i))                return false;         return false;    }     // Function for find difference of larger numbers    static String findDiff(String str1, String str2)    {        // Before proceeding further, make sure str1        // is not smaller        if (isSmaller(str1, str2)) {            String t = str1;            str1 = str2;            str2 = t;        }         // 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        str1 = new StringBuilder(str1).reverse().toString();        str2 = new StringBuilder(str2).reverse().toString();         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                = ((int)(str1.charAt(i) - '0')                   - (int)(str2.charAt(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 += (char)(sub + '0');        }         // subtract remaining digits of larger number        for (int i = n2; i < n1; i++) {            int sub = ((int)(str1.charAt(i) - '0') - carry);             // if the sub value is -ve, then make it            // positive            if (sub < 0) {                sub = sub + 10;                carry = 1;            }            else                carry = 0;             str += (char)(sub + '0');        }         // reverse resultant string        return new StringBuilder(str).reverse().toString();    }     // Driver code    public static void main(String[] args)    {        String str1 = "978";        String str2 = "12977";         // Function call        System.out.println(findDiff(str1, str2));         String s1 = "100";        String s2 = "1000000";               // Function call        System.out.println(findDiff(s1, s2));    }} // This code is contributed by mits
# Python 3 program to find difference of two large numbers. # Returns true if str1 is smaller than str2.  def isSmaller(str1, str2):     # Calculate lengths of both string    n1 = len(str1)    n2 = len(str2)     if (n1 < n2):        return True    if (n2 < n1):        return False     for i in range(n1):        if (str1[i] < str2[i]):            return True        elif (str1[i] > str2[i]):            return False     return False # Function for find difference of larger numbers  def findDiff(str1, str2):     # Before proceeding further, make sure str1    # is not smaller    if (isSmaller(str1, str2)):        temp = str1        str1 = str2        str2 = temp     # Take an empty string for storing result    str3 = ""     # Calculate length of both string    n1 = len(str1)    n2 = len(str2)     # Reverse both of strings    str1 = str1[::-1]    str2 = str2[::-1]     carry = 0     # Run loop till small string length    # and subtract digit of str1 to str2    for i in range(n2):         # Do school mathematics, compute difference of        # current digits         sub = ((ord(str1[i])-ord('0'))-(ord(str2[i])-ord('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         str3 = str3+str(sub)     # subtract remaining digits of larger number    for i in range(n2, n1):         sub = ((ord(str1[i])-ord('0')) - carry)         # if the sub value is -ve, then make it positive        if (sub < 0):             sub = sub + 10            carry = 1         else:            carry = 0         str3 = str3+str(sub)     # reverse resultant string    str3 = str3[::-1]     return str3  # Driver codeif __name__ == "__main__":    str1 = "978"    str2 = "12977"         # Function call    print(findDiff(str1, str2))     s1 = "100"    s2 = "1000000"         # Function call    print(findDiff(s1, s2)) # This code is contributed by ChitraNayal
// C# program to find difference of two large numbers.using System;using System.Collections; class GFG {     // Returns true if str1 is smaller than str2.    static 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    static string findDiff(string str1, string str2)    {        // Before proceeding further, make sure str1        // is not smaller        if (isSmaller(str1, str2)) {            string t = str1;            str1 = str2;            str2 = t;        }         // 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        char[] ch1 = str1.ToCharArray();        Array.Reverse(ch1);        str1 = new string(ch1);        char[] ch2 = str2.ToCharArray();        Array.Reverse(ch2);        str2 = new string(ch2);         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 = ((int)(str1[i] - '0')                       - (int)(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 += (char)(sub + '0');        }         // subtract remaining digits of larger number        for (int i = n2; i < n1; i++) {            int sub = ((int)(str1[i] - '0') - carry);             // if the sub value is -ve, then make it            // positive            if (sub < 0) {                sub = sub + 10;                carry = 1;            }            else                carry = 0;             str += (char)(sub + '0');        }         // reverse resultant string        char[] ch3 = str.ToCharArray();        Array.Reverse(ch3);        return new string(ch3);    }     // Driver code    public static void Main()    {        string str1 = "978";        string str2 = "12977";         // Function call        Console.WriteLine(findDiff(str1, str2));         string s1 = "100";        string s2 = "1000000";               // Function call        Console.WriteLine(findDiff(s1, s2));    }} // This code is contributed by mits
<?php// PHP program to find difference of two large numbers. // Returns true if str1 is smaller than str2.function isSmaller($str1, $str2){    // Calculate lengths of both string    $n1 = strlen($str1);    $n2 = strlen($str2);     if ($n1 < $n2)    return true;    if ($n2 < $n1)    return false;     for ($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 numbersfunction findDiff($str1, $str2){    // Before proceeding further, make sure str1    // is not smaller    if (isSmaller($str1, $str2)){        $t=$str1;        $str1=$str2;        $str2=$t;    }     // Take an empty string for storing result    $str = "";     // Calculate length of both string    $n1 = strlen($str1);    $n2 = strlen($str2);     // Reverse both of strings    $str1=strrev($str1);    $str2=strrev($str2);         $carry = 0;     // Run loop till small string length    // and subtract digit of str1 to str2    for ($i=0; $i<$n2; $i++)    {        // Do school mathematics, compute difference of        // current digits                 $sub=((ord($str1[$i])-ord('0'))-(ord($str2[$i])-ord('0'))-$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;         $str.=chr($sub+48);    }     // subtract remaining digits of larger number    for ($i=$n2; $i<$n1; $i++)    {        $sub = ((ord($str1[$i])-ord('0')) - $carry);                 // if the sub value is -ve, then make it positive        if ($sub < 0)        {            $sub = $sub + 10;            $carry = 1;        }        else            $carry = 0;                     $str.=chr($sub+48);    }     // reverse resultant string    $str=strrev($str);     return $str;} // Driver code     $str1 = "978";    $str2 = "12977";     // Function call    echo findDiff($str1, $str2)."\n";         $s1 = "100";    $s2 = "1000000";     // Function call    echo findDiff($s1,$s2);     // This code is contributed by mits?>
<script> // Javascript program to find difference// of two large numbers.     // Returns true if str1 is smaller than str2.    function isSmaller(str1,str2)    {        // Calculate lengths of both string        let n1 = str1.length, n2 = str2.length;        if (n1 < n2)            return true;        if (n2 < n1)            return false;          for (let 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    function findDiff(str1,str2)    {        // Before proceeding further,        // make sure str1        // is not smaller        if (isSmaller(str1, str2)) {            let t = str1;            str1 = str2;            str2 = t;        }          // Take an empty string for storing result        let str = "";          // Calculate length of both string        let n1 = str1.length, n2 = str2.length;          // Reverse both of strings        str1 = str1.split("").reverse().join("")        str2 = str2.split("").reverse().join("")          let carry = 0;          // Run loop till small string length        // and subtract digit of str1 to str2        for (let i = 0; i < n2; i++)        {            // Do school mathematics,            // compute difference of            // current digits            let sub                = ((str1[i].charCodeAt(0) -                '0'.charCodeAt(0))                   - (str2[i].charCodeAt(0) -                   '0'.charCodeAt(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 += String.fromCharCode(sub +            '0'.charCodeAt(0));        }          // subtract remaining digits of larger number        for (let i = n2; i < n1; i++) {            let sub = ((str1[i].charCodeAt(0) -            '0'.charCodeAt(0)) - carry);              // if the sub value is -ve, then make it            // positive            if (sub < 0) {                sub = sub + 10;                carry = 1;            }            else                carry = 0;              str += String.fromCharCode(sub +            '0'.charCodeAt(0));        }          // reverse resultant string        return str.split("").reverse().join("")    }         // Driver code         let str1 = "978";    let str2 = "12977";         document.write(findDiff(str1, str2)+"<br>");          let s1 = "100";    let s2 = "1000000";    document.write(findDiff(s1, s2)+"<br>");         // This code is contributed by rag2127 </script>
11999
0999900
Time Complexity: O(n1 + n2)
Auxiliary Space: O(max(n1, n2))Optimized solution : We can avoid the first two string reverse operations by traversing them from the end. 
Below is the optimized solution. 
C++
Java
Python3
C#
PHP
Javascript
// 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 numbersstring 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 codeint main(){    string str1 = "88";    string str2 = "1079";       // Function call    cout << findDiff(str1, str2);    return 0;}
// Java program to find difference of two large numbers. class GFG {     // Returns true if str1 is smaller than str2,    // else false.    static boolean 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.charAt(i) < str2.charAt(i))                return true;            else if (str1.charAt(i) > str2.charAt(i))                return false;        }        return false;    }     // Function for finding difference of larger numbers    static String findDiff(String str1, String str2)    {        // Before proceeding further, make sure str1        // is not smaller        if (isSmaller(str1, str2)) {            String t = str1;            str1 = str2;            str2 = t;        }         // 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                = (((int)str1.charAt(i + diff) - (int)'0')                   - ((int)str2.charAt(i) - (int)'0')                   - carry);            if (sub < 0) {                sub = sub + 10;                carry = 1;            }            else                carry = 0;             str += String.valueOf(sub);        }         // subtract remaining digits of str1[]        for (int i = n1 - n2 - 1; i >= 0; i--) {            if (str1.charAt(i) == '0' && carry > 0) {                str += "9";                continue;            }            int sub = (((int)str1.charAt(i) - (int)'0')                       - carry);            if (i > 0 || sub > 0) // remove preceding 0's                str += String.valueOf(sub);            carry = 0;        }         // reverse resultant string        return new StringBuilder(str).reverse().toString();    }     // Driver code    public static void main(String[] args)    {        String str1 = "88";        String str2 = "1079";               // Function call        System.out.println(findDiff(str1, str2));    }} // This code is contributed by mits
# Python3 program to find difference# of two large numbers. # Returns true if str1 is smaller than# str2, else false.def isSmaller(str1, str2):         # Calculate lengths of both string    n1 = len(str1)    n2 = len(str2)     if (n1 < n2):        return True    if (n2 < n1):        return False     for i in range(n1):        if (str1[i] < str2[i]):            return True        elif (str1[i] > str2[i]):            return False                 return False # Function for finding difference# of larger numbersdef findDiff(str1, str2):         # Before proceeding further,    # make sure str1 is not smaller    if (isSmaller(str1, str2)):        str1, str2 = str2, str1     # Take an empty string for    # storing result    Str = ""         # Calculate lengths of both string    n1 = len(str1)    n2 = len(str2)    diff = n1 - n2         # Initially take carry zero    carry = 0         # Traverse from end of both strings    for i in range(n2 - 1, -1, -1):                 # Do school mathematics, compute        # difference of current digits        # and carry        sub = ((ord(str1[i + diff]) - ord('0')) -               (ord(str2[i]) - ord('0')) - carry)         if (sub < 0):            sub += 10            carry = 1        else:            carry = 0         Str += chr(sub + ord('0'))         # Subtract remaining digits of str1[]    for i in range(n1 - n2 - 1, -1, -1):        if (str1[i] == '0' and carry):            Str += '9'            continue                     sub = (ord(str1[i]) - ord('0')) - carry                 # Remove preceding 0's        if (i > 0 or sub > 0):            Str += chr(sub + ord('0'))                     carry = 0     # Reverse resultant string    Str = Str[::-1]         return Str # Driver codestr1 = "88"str2 = "1079" # Function callprint(findDiff(str1, str2)) # This code is contributed by avanitrachhadiya2155
// C# program to find difference of// two large numbers.using System; class GFG {     // Returns true if str1 is smaller    // than str2, else false.    static 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    static string findDiff(string str1, string str2)    {        // Before proceeding further,        // make sure str1 is not smaller        if (isSmaller(str1, str2)) {            string t = str1;            str1 = str2;            str2 = t;        }         // 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 = (((int)str1[i + diff] - (int)'0')                       - ((int)str2[i] - (int)'0') - carry);            if (sub < 0) {                sub = sub + 10;                carry = 1;            }            else                carry = 0;             str += sub.ToString();        }         // subtract remaining digits of str1[]        for (int i = n1 - n2 - 1; i >= 0; i--) {            if (str1[i] == '0' && carry > 0) {                str += "9";                continue;            }            int sub = (((int)str1[i] - (int)'0') - carry);            if (i > 0 || sub > 0) // remove preceding 0's                str += sub.ToString();            carry = 0;        }         // reverse resultant string        char[] aa = str.ToCharArray();        Array.Reverse(aa);        return new string(aa);    }     // Driver code    public static void Main()    {        String str1 = "88";        String str2 = "1079";         // Function call        Console.WriteLine(findDiff(str1, str2));    }} // This code is contributed by mits
<?php// PHP program to find difference of two// large numbers. // Returns true if str1 is smaller than// str2, else false.function isSmaller($str1, $str2){    // Calculate lengths of both string    $n1 = strlen($str1);    $n2 = strlen($str2);     if ($n1 < $n2)        return true;    if ($n2 < $n1)        return false;     for ($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 numbersfunction findDiff($str1, $str2){    // Before proceeding further, make    // sure str1 is not smaller    if (isSmaller($str1, $str2))    {        $t = $str1;        $str1 = $str2;        $str2 = $t;    }     // Take an empty string for storing result    $str = "";     // Calculate lengths of both string    $n1 = strlen($str1);    $n2 = strlen($str2);    $diff = $n1 - $n2;     // Initially take carry zero    $carry = 0;     // Traverse from end of both strings    for ($i = $n2 - 1; $i >= 0; $i--)    {        // Do school mathematics, compute        // difference of current digits and carry        $sub = ((ord($str1[$i + $diff]) - ord('0')) -                (ord($str2[$i]) - ord('0')) - $carry);        if ($sub < 0)        {            $sub = $sub + 10;            $carry = 1;        }        else            $carry = 0;         $str.=chr($sub + ord("0"));    }     // subtract remaining digits of str1[]    for ($i = $n1 - $n2 - 1; $i >= 0; $i--)    {        if ($str1[$i] == '0' && $carry > 0)        {            $str.="9";            continue;        }        $sub = (ord($str1[$i]) - ord('0') - $carry);        if ($i > 0 || $sub > 0) // remove preceding 0's            $str.=chr($sub + ord("0"));        $carry = 0;     }     // reverse resultant string    return strrev($str); } // Driver code$str1 = "88";$str2 = "1079"; // Function callprint(findDiff($str1, $str2)); // This code is contributed by chandan_jnu?>
<script>     // JavaScript program to find difference    // of two large numbers.         // Returns true if str1 is smaller    // than str2, else false.    function isSmaller(str1, str2)    {        // Calculate lengths of both string        let n1 = str1.length, n2 = str2.length;          if (n1 < n2)            return true;        if (n2 < n1)            return false;          for (let i = 0; i < n1; i++) {            if (str1[i].charCodeAt() < str2[i].charCodeAt())                return true;            else if (str1[i].charCodeAt() > str2[i].charCodeAt())                return false;        }        return false;    }      // Function for finding difference of    // larger numbers    function findDiff(str1, str2)    {        // Before proceeding further,        // make sure str1 is not smaller        if (isSmaller(str1, str2)) {            let t = str1;            str1 = str2;            str2 = t;        }          // Take an empty string for        // storing result        let str = "";          // Calculate lengths of both string        let n1 = str1.length, n2 = str2.length;        let diff = n1 - n2;          // Initially take carry zero        let carry = 0;          // Traverse from end of both strings        for (let i = n2 - 1; i >= 0; i--) {            // Do school mathematics, compute            // difference of current digits and carry            let sub = ((str1[i + diff].charCodeAt() -                       '0'.charCodeAt())                   - (str2[i].charCodeAt() -                     '0'.charCodeAt()) - carry);            if (sub < 0) {                sub = sub + 10;                carry = 1;            }            else                carry = 0;              str += sub.toString();        }          // subtract remaining digits of str1[]        for (let i = n1 - n2 - 1; i >= 0; i--) {            if (str1[i] == '0' && carry > 0) {                str += "9";                continue;            }            let sub = ((str1[i].charCodeAt() -                       '0'.charCodeAt()) - carry);            if (i > 0 || sub > 0) // remove preceding 0's                str += sub.toString();            carry = 0;        }          // reverse resultant string        let aa = str.split('');        aa.reverse();        return aa.join("");    }         let str1 = "88";    let str2 = "1079";     // Function call    document.write(findDiff(str1, str2));     </script>
991
Time complexity : O(n1 + n2)
Auxiliary Space: O(max(n1, n2))
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