Sum of two numbers where one number is represented as array of digits

Difficulty Level : Easy
Last Updated : 06 Jun, 2021

Given an array arr[] of digits and an integer K, the task is to find num(arr) + K where num(arr) is the number formed by concatenating all the digits of the array.

Examples:

Input: arr[] = {2, 7, 4}, K = 181
Output: 455
274 + 181 = 455
Input: arr[] = {6}, K = 815
Output: 821
6 + 815 = 821

Approach: Start traversing the digits array from the end and start adding the digits of K one by one to the current digit, if any carry is generated then add it to the next addition of digits. After all the digits of K have been added, start traversing the digits array from the left and start printing the elements which on concatenation will give the resultant number.

Below is the implementation of the above approach:

C++

// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
 
// Function to return the vector containing the answer
vector<int> addToArrayForm(vector<int>& A, int K)
{
 
    // Vector v is to store each digits sum
    // and vector ans is to store the answer
    vector<int> v, ans;
 
    // No carry in the beginning
    int rem = 0;
 
    int i = 0;
 
    // Start loop from the end
    // and take element one by one
    for (i = A.size() - 1; i >= 0; i--) {
 
        // Array index and last digit of number
        int my = A[i] + K % 10 + rem;
        if (my > 9) {
 
            // Maintain carry of summation
            rem = 1;
 
            // Push the digit value into the array
            v.push_back(my % 10);
        }
        else {
            v.push_back(my);
            rem = 0;
        }
        K = K / 10;
    }
 
    // K value is greater then 0
    while (K > 0) {
 
        // Push digits of K one by one in the array
        int my = K % 10 + rem;
        v.push_back(my % 10);
 
        // Also maintain carry with summation
        if (my / 10 > 0)
            rem = 1;
        else
            rem = 0;
        K = K / 10;
    }
 
    if (rem > 0)
        v.push_back(rem);
 
    // Reverse the elements of vector v
    // and store it in vector ans
    for (int i = v.size() - 1; i >= 0; i--)
        ans.push_back(v[i]);
 
    return ans;
}
 
// Driver code
int main()
{
    vector<int> A{ 2, 7, 4 };
    int K = 181;
    vector<int> ans = addToArrayForm(A, K);
 
    // Print the answer
    for (int i = 0; i < ans.size(); i++)
        cout << ans[i];
 
    return 0;
}

Java

// Java implementation of the approach
import java.util.*;
 
class GFG
{
    // Function to return the vector containing the answer
    static ArrayList<Integer> addToArrayForm(ArrayList<Integer> A, int K)
    {
     
        // ArrayList v is to store each digits sum
        // and ArrayList ans is to store the answer
        ArrayList<Integer> v = new ArrayList<Integer>();
        ArrayList<Integer> ans = new ArrayList<Integer>();
         
        // No carry in the beginning
        int rem = 0;
     
        int i = 0;
     
        // Start loop from the end
        // and take element one by one
        for (i = A.size() - 1; i >= 0; i--)
        {
     
            // Array index and last digit of number
            int my = A.get(i) + K % 10 + rem;
            if (my > 9)
            {
     
                // Maintain carry of summation
                rem = 1;
     
                // Push the digit value into the array
                v.add(my % 10);
            }
            else
            {
                v.add(my);
                rem = 0;
            }
            K = K / 10;
        }
     
        // K value is greater then 0
        while (K > 0)
        {
     
            // Push digits of K one by one in the array
            int my = K % 10 + rem;
            v.add(my % 10);
     
            // Also maintain carry with summation
            if (my / 10 > 0)
                rem = 1;
            else
                rem = 0;
            K = K / 10;
        }
     
        if (rem > 0)
            v.add(rem);
     
        // Reverse the elements of vector v
        // and store it in vector ans
        for (int j = v.size() - 1; j >= 0; j--)
            ans.add(v.get(j));
     
        return ans;
    }
     
    // Driver code
    public static void main (String[] args)
    {
        ArrayList<Integer> A = new ArrayList<Integer>();
        A.add(2);
        A.add(7);
        A.add(4);
         
         
        int K = 181;
        ArrayList<Integer> ans = addToArrayForm(A, K);
     
        // Print the answer
        for (int i = 0; i < ans.size(); i++)
            System.out.print(ans.get(i));
     
    }
}
 
// This code is contributed by ihritik

Python3

# Python3 implementation of the approach
 
# Function to return the vector
# containing the answer
def addToArrayForm(A, K):
 
    # Vector v is to store each digits sum
    # and vector ans is to store the answer
    v, ans = [], []
 
    # No carry in the beginning
    rem, i = 0, 0
 
    # Start loop from the end
    # and take element one by one
    for i in range(len(A) - 1, -1, -1):
 
        # Array index and last digit of number
        my = A[i] + (K % 10) + rem
        if my > 9:
 
            # Maintain carry of summation
            rem = 1
 
            # Push the digit value into the array
            v.append(my % 10)
         
        else:
            v.append(my)
            rem = 0
         
        K = K // 10
     
    # K value is greater then 0
    while K > 0:
 
        # Push digits of K one by one in the array
        my = (K % 10) + rem
        v.append(my % 10)
 
        # Also maintain carry with summation
        if my // 10 > 0:
            rem = 1
        else:
            rem = 0
         
        K = K // 10
     
    if rem > 0:
        v.append(rem)
 
    # Reverse the elements of vector v
    # and store it in vector ans
    for i in range(len(v) - 1, -1, -1):
        ans.append(v[i])
 
    return ans
 
# Driver code
if __name__ == "__main__":
 
    A = [2, 7, 4]
    K = 181
    ans = addToArrayForm(A, K)
 
    # Print the answer
    for i in range(0, len(ans)):
        print(ans[i], end = "")
 
# This code is contributed by Rituraj Jain

C#

// C# implementation of the approach
using System;
using System.Collections;
 
class GFG
{
    // Function to return the vector containing the answer
    static ArrayList addToArrayForm(ArrayList A, int K)
    {
     
        // ArrayList v is to store each digits sum
        // and ArrayList ans is to store the answer
        ArrayList v = new ArrayList();
        ArrayList ans = new ArrayList();
         
        // No carry in the beginning
        int rem = 0;
     
        int i = 0;
     
        // Start loop from the end
        // and take element one by one
        for (i = A.Count - 1; i >= 0; i--)
        {
     
            // Array index and last digit of number
            int my = (int)A[i] + K % 10 + rem;
            if (my > 9)
            {
     
                // Maintain carry of summation
                rem = 1;
     
                // Push the digit value into the array
                v.Add(my % 10);
            }
            else
            {
                v.Add(my);
                rem = 0;
            }
            K = K / 10;
        }
     
        // K value is greater then 0
        while (K > 0)
        {
     
            // Push digits of K one by one in the array
            int my = K % 10 + rem;
            v.Add(my % 10);
     
            // Also maintain carry with summation
            if (my / 10 > 0)
                rem = 1;
            else
                rem = 0;
            K = K / 10;
        }
     
        if (rem > 0)
            v.Add(rem);
     
        // Reverse the elements of vector v
        // and store it in vector ans
        for (int j = v.Count - 1; j >= 0; j--)
            ans.Add((int)v[j]);
     
        return ans;
    }
     
    // Driver code
    static void Main()
    {
        ArrayList A = new ArrayList();
        A.Add(2);
        A.Add(7);
        A.Add(4);
         
        int K = 181;
        ArrayList ans = addToArrayForm(A, K);
     
        // Print the answer
        for (int i = 0; i < ans.Count; i++)
            Console.Write((int)ans[i]);
    }
}
 
// This code is contributed by mits

PHP

<?php
// Php implementation of the approach
 
// Function to return the vector containing the answer
function addToArrayForm($A, $K)
{
 
    // Vector v is to store each digits sum
    // and vector ans is to store the answer
    $v = array();
    $ans = array();
 
    // No carry in the beginning
    $rem = 0;
 
    $i = 0;
 
    // Start loop from the end
    // and take element one by one
    for ($i = count($A) - 1; $i >= 0; $i--)
    {
 
        // Array index and last digit of number
        $my = $A[$i] + $K % 10 + $rem;
        if ($my > 9)
        {
 
            // Maintain carry of summation
            $rem = 1;
 
            // Push the digit value into the array
            array_push($v,$my % 10);
        }
        else
        {
            array_push($v,$my);
            $rem = 0;
        }
        $K = floor($K / 10);
    }
 
    // K value is greater then 0
    while ($K > 0)
    {
 
        // Push digits of K one by one in the array
        $my = $K % 10 + $rem;
         
        array_push($v,$my % 10);
 
        // Also maintain carry with summation
        if ($my / 10 > 0)
            $rem = 1;
        else
            $rem = 0;
             
        $K = floor($K / 10);
    }
 
    if ($rem > 0)
        array_push($v,$rem);
 
    // Reverse the elements of vector v
    // and store it in vector ans
    for ($i = count($v) - 1; $i >= 0; $i--)
        array_push($ans,$v[$i]);
 
    return $ans;
}
 
// Driver code
$A = array( 2, 7, 4 );
$K = 181;
$ans = addToArrayForm($A, $K);
 
// Print the answer
for ($i = 0; $i < count($ans); $i++)
    echo $ans[$i];
     
// This code is contributed by Ryuga
?>

Javascript

<script>
 
// Javascript implementation of the approach
 
// Function to return the vector
// containing the answer
function addToArrayForm(A, K)
{
     
    // ArrayList v is to store each digits sum
    // and ArrayList ans is to store the answer
    let v = [];
    let ans = [];
       
    // No carry in the beginning
    let rem = 0;
   
    let i = 0;
   
    // Start loop from the end
    // and take element one by one
    for(i = A.length - 1; i >= 0; i--)
    {
         
        // Array index and last digit of number
        let my = A[i] + K % 10 + rem;
        if (my > 9)
        {
             
            // Maintain carry of summation
            rem = 1;
   
            // Push the digit value into the array
            v.push(my % 10);
        }
        else
        {
            v.push(my);
            rem = 0;
        }
        K = parseInt(K / 10, 10);
    }
   
    // K value is greater then 0
    while (K > 0)
    {
   
        // Push digits of K one by one in the array
        let my = K % 10 + rem;
        v.push(my % 10);
   
        // Also maintain carry with summation
        if (parseInt(my / 10, 10) > 0)
            rem = 1;
        else
            rem = 0;
             
        K = parseInt(K / 10, 10);
    }
   
    if (rem > 0)
        v.push(rem);
   
    // Reverse the elements of vector v
    // and store it in vector ans
    for(let j = v.length - 1; j >= 0; j--)
        ans.push(v[j]);
   
    return ans;
}
 
// Driver code
let A = [];
A.push(2);
A.push(7);
A.push(4);
 
let K = 181;
let ans = addToArrayForm(A, K);
 
// Print the answer
for(let i = 0; i < ans.length; i++)
    document.write(ans[i]);
     
// This code is contributed by divyeshrabadiya07
 
</script>

Output:

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