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Add 1 to number represented as array | Recursive Approach

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  • Difficulty Level : Medium
  • Last Updated : 27 Jul, 2022
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Given an array which represents a number, add 1 to the array. Suppose an array contain elements [1, 2, 3, 4] then the array represents decimal number 1234 and hence adding 1 to this would result 1235. So new array will be [1, 2, 3, 5].

Examples:

Input :  [1, 2, 3, 4]
Output : [1, 2, 3, 5]

Input :  [1, 2, 9, 9]
Output : [1, 3, 0, 0]

Input:  [9, 9, 9, 9]
Output: [1, 0, 0, 0, 0]

Approach : 

  1. Add 1 to the last element of the array, if it is less than 9. 
  2. If it is 9, then make it 0 and recurse for the remaining element of the array.

Implementation:

C++




// C++ Program to add 1 to an array
// representing a number
#include <bits/stdc++.h>
using namespace std;
 
// function to add one and print the array
void sum(int arr[], int n)
{
     
 int i = n;
 
 // if array element is less than 9, then
 // simply add 1 to this.
 if(arr[i] < 9)
 {
     arr[i] = arr[i] + 1;
     return;
 }
 
 // if array element is greater than 9,
 // replace it with 0 and decrement i
    arr[i] = 0;
    i--;
 
    // recursive function
    sum(arr, i);
}
 
// driver code
int main()
{
    // number of elements in array
    int n = 4;
 
    // array elements, index of array
    // should be 1 based, hence, 0 is
    // added here at arr[0]
    int arr[] = {0, 1, 9, 3, 9};
 
    // function calling
    sum(arr, n);
     
    // If 1 was appended at head
    // of array then, print it
    if(arr[0] > 0)
        cout << arr[0] << ", ";
 
    // print the array elements
    // after adding one
    for(int i = 1; i <= n; i++)
    {
            cout << arr[i];
             
            if(i < n)
                cout << ", ";
    }
    return 0;
}

Java




// Java Program to add 1 to an array
// representing a number
import java.io.*;
   
public class GFG {
   
    // function to add one and print the array
    void sum(int[] arr, int n)
    {
        int i = n;
   
        // if array element is less than 9, then
        // simply add 1 to this.
        if (arr[i] < 9) {
            arr[i] = arr[i] + 1;
            return;
        }
           
        // if array element is greater than 9,
        // replace it with 0 and decrement i
        arr[i] = 0;
        i--;
         
        // recursive function
        sum(arr, i);
    }
   
    // driver code
    static public void main(String[] args)
    {
        GFG obj = new GFG();
           
        // number of elements in array
        int n = 4;
   
        // array elements, index of array
        // should be 1 based, hence, 0 is
        // added here at arr[0]
        int arr[] = {0, 1, 9, 3, 9};
   
        obj.sum(arr, n);
   
        // If 1 was appended at head
        // of array then, print it
        if (arr[0] > 0)
            System.out.print(arr[0] + ", ");
 
        int i;
        for (i = 1; i <= n; i++) {
            System.out.print(arr[i]);
   
            if (i < n)
                System.out.print(", ");
        }
 
    }
}
 
// This code is contributed by vt_m.

Python 3




# Python 3 Program to add 1 to an
# array representing a number
 
# function to add one and print
# the array
def sum(arr, n):
 
    i = n
     
    # if array element is less than
    # 9, then simply add 1 to this.
    if(arr[i] < 9):
     
        arr[i] = arr[i] + 1
        return
     
    # if array element is greater
    # than 9, replace it with 0
    # and decrement i
    arr[i] = 0
    i -= 1
     
    # recursive function
    sum(arr, i)
     
     
# driver code
# number of elements in array
n = 4
 
# array elements, index of array
# should be 1 based, hence, 0 is
# added here at arr[0]
arr = [0, 1, 9, 3, 9]
 
# function calling
sum(arr, n)
 
# If 1 was appended at head
# of array then, print it
if(arr[0] > 0):
    print(arr[0], ", ", end="")
     
# print the array elements
# after adding one
for i in range(1, n+1):
     
    print(arr[i], end="")
    if(i < n):
        print(", ", end="")
 
# This code is contributed by
# Smitha Semwal

C#




// C# Program to add 1 to an array
// representing a number
using System;
 
public class GFG {
     
    // function to add one and print the array
    void sum(int []arr, int n){
         
    int i = n;
 
    // if array element is less than 9, then
    // simply add 1 to this.
    if(arr[i] < 9)
    {
      arr[i] = arr[i] + 1;
      return;
    }
 
    // if array element is greater than 9,
    // replace it with 0 and decrement i
    arr[i] = 0;
    i--;
 
    // recursive function
    sum(arr, i);
}
 
    // driver code
    static public void Main ()
    {
      GFG obj =new GFG();
         
    // number of elements in array
    int n = 4;
 
    // array elements, index of array
    // should be 1 based, hence, 0 is
    // added here at arr[0]
    int []arr = {0, 1, 9, 3, 9};
 
    // function calling
    obj.sum(arr, n);
     
    // If 1 was appended at head
    // of array then, print it
    if(arr[0] > 0)
        Console.Write(arr[0] + ", ");
    int i;
    // print the array elements
    // after adding one
    for( i = 1; i <= n; i++)
    {
        Console.Write(arr[i]);
             
        if(i < n)
            Console.Write(", ");
    }
 
    }
}

Javascript




<script>
// JavaScript Program to add 1 to an array
// representing a number
 
// function to add one and print the array
function sum(arr, n)
{
     
 var i = n;
 
 // if array element is less than 9, then
 // simply add 1 to this.
 if(arr[i] < 9)
 {
     arr[i] = arr[i] + 1;
     return;
 }
 
 // if array element is greater than 9,
 // replace it with 0 and decrement i
    arr[i] = 0;
    i--;
 
    // recursive function
    sum(arr, i);
}
 
// Driver code
 
    // number of elements in array
    var n = 4;
 
    // array elements, index of array
    // should be 1 based, hence, 0 is
    // added here at arr[0]
    arr = [0, 1, 9, 3, 9]
 
    // function calling
    sum(arr, n);
     
    // If 1 was appended at head
    // of array then, print it
    if(arr[0] > 0)
        document.write(arr[0] + ", ");
 
    // print the array elements
    // after adding one
    for(var i = 1; i <= n; i++)
    {
            document.write(arr[i]);    
            if(i < n)
                document.write(", ");
    }
 
// This code is contributed by rdtank.
    </script>

Output

1, 9, 4, 0

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