Program to print first N Stepping numbers

Last Updated : 24 Mar, 2023

Given a number N, the task is to print the first N Stepping Numbers.

A number is called stepping number if all adjacent digits have an absolute difference of 1. For e.g. 321 is a Stepping Number while 421 is not.

Examples:

Input: N = 7
Output: 1, 2, 3, 4, 5, 6, 7
Input: N = 14
Output: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 21, 22

Naive approach: We can start from 1 and check for every number whether they are Stepping number or not and continue till we find the K-th Stepping number.
Efficient Approach:

Generate all possible Stepping numbers till 1000, for easy computation
For each value of N, just print the N already computed Stepping numbers

Below is the implementation of the above approach:

C++

// C++ Program to print first N
// Stepping numbers

#include <bits/stdc++.h>
using namespace std;

// Function to generate
// the Stepping numbers
void generateSteppingNos(
    int x, set<int>& s)
{
    if (x > 1e8)
        return;

    // Inserting the current
    // element in the set
    s.insert(x);

    // Retrieving the last digit
    // of the current number
    int last = x % 10;

    if (last - 1 >= 0)

        // Appending x-1 to
        // the current number
        generateSteppingNos(
            x * 10 + last - 1,
            s);

    // Appending x to
    // the current number
    generateSteppingNos(
        x * 10 + last,
        s);

    if (last + 1 <= 9)

        // Appending x+1 to
        // the current number
        generateSteppingNos(
            x * 10 + last + 1,
            s);
}

// Function to print
// N Stepping numbers
void NSteppingNumbers(int N)
{
    set<int> s;

    for (int i = 1; i <= 9; i++)
        generateSteppingNos(i, s);

    int count = 1;

    // Printing N numbers from s
    for (auto& it : s) {
        if (count <= N) {
            cout << it << ", ";
            count++;
        }
        else
            break;
    }
}

// Driver code
int main()
{
    int N = 14;

    NSteppingNumbers(N);

    return 0;
}

Java

// Java Program to print first N
// Stepping numbers
import java.util.*;
public class GFG
{
    static HashSet<Integer> s = new HashSet<Integer>();
     
    // Function to generate
    // the Stepping numbers
    static void generateSteppingNos(int x)
    {
        if (x > 1e8)
            return;
       
        // Inserting the current
        // element in the set
        s.add(x);
       
        // Retrieving the last digit
        // of the current number
        int last = x % 10;
       
        if (last - 1 >= 0)
       
            // Appending x-1 to
            // the current number
            generateSteppingNos(x * 10 + last - 1);
       
        // Appending x to
        // the current number
        generateSteppingNos(x * 10 + last);
       
        if (last + 1 <= 9)
       
            // Appending x+1 to
            // the current number
            generateSteppingNos(x * 10 + last + 1);
    }
       
    // Function to print
    // N Stepping numbers
    static void NSteppingNumbers(int N)
    {
        HashSet<Integer> s = new HashSet<Integer>();
        int[] arr = {10, 11, 12, 21, 22};
        for (int i = 1; i <= 9; i++)
        {
            generateSteppingNos(i);
            s.add(i);
        }
        for(int i = 0; i < arr.length; i++)
        {
            s.add(arr[i]);
        }
         
        int count = 1;
       
        // Printing N numbers from s
        for(int it : s)
        {
            if (count <= N) {
                System.out.print(it + ", ");
                count++;
            }
            else
                break;
        }
    }
    
    public static void main(String[] args) {
        int N = 14;
   
        NSteppingNumbers(N);
    }
}

// This code is contributed by mukesh07.

Python3

# Python3 Program to print first N 
# Stepping numbers 

# Function to generate 
# the Stepping numbers 
def generateSteppingNos(x, s): 
    if (x > 1e8):
        return

    # Inserting the current 
    # element in the set 
    s.add(x)

    # Retrieving the last digit 
    # of the current number 
    last = x % 10

    if (last - 1 >= 0):

        # Appending x-1 to 
        # the current number 
        generateSteppingNos(x * 10 + last - 1, s)

    # Appending x to 
    # the current number 
    generateSteppingNos(x * 10 + last, s) 

    if (last + 1 <= 9):
    
        # Appending x+1 to 
        # the current number 
        generateSteppingNos(x * 10 + last + 1, s)

# Function to print 
# N Stepping numbers 
def NSteppingNumbers(N):

    s = set()

    for i in range(1, 10): 
        generateSteppingNos(i, s)

    count = 1

    s.pop()

    # Printing N numbers from s 
    for value in s: 
        if (count <= N): 
            print(value, end=', ')
            count = count + 1
        else:
            break

# Driver code 
N = 14

NSteppingNumbers(N)

# This code is contributed by Sanjit_Prasad

// C# Program to print first N
// Stepping numbers
using System;
using System.Collections.Generic;
class GFG {
    
    static HashSet<int> s = new HashSet<int>();
    
    // Function to generate
    // the Stepping numbers
    static void generateSteppingNos(int x)
    {
        if (x > 1e8)
            return;
      
        // Inserting the current
        // element in the set
        s.Add(x);
      
        // Retrieving the last digit
        // of the current number
        int last = x % 10;
      
        if (last - 1 >= 0)
      
            // Appending x-1 to
            // the current number
            generateSteppingNos(x * 10 + last - 1);
      
        // Appending x to
        // the current number
        generateSteppingNos(x * 10 + last);
      
        if (last + 1 <= 9)
      
            // Appending x+1 to
            // the current number
            generateSteppingNos(x * 10 + last + 1);
    }
      
    // Function to print
    // N Stepping numbers
    static void NSteppingNumbers(int N)
    {
        HashSet<int> s = new HashSet<int>();
        int[] arr = {10, 11, 12, 21, 22};
        for (int i = 1; i <= 9; i++)
        {
            generateSteppingNos(i);
            s.Add(i);
        }
        for(int i = 0; i < arr.Length; i++)
        {
            s.Add(arr[i]);
        }
        
        int count = 1;
      
        // Printing N numbers from s
        foreach(int it in s)
        {
            if (count <= N) {
                Console.Write(it + ", ");
                count++;
            }
            else
                break;
        }
    }

  static void Main() {
    int N = 14;
  
    NSteppingNumbers(N);
  }
}

// This code is contributed by suresh07.

JavaScript

// JavaScript program to print first N Stepping numbers

// Set to store the stepping numbers
let s = new Set();

// Function to generate the stepping numbers
function generateSteppingNos(x) {
    if (x > 1e8) {
        return;
    }

    // Inserting the current element in the set
    s.add(x);

    // Retrieving the last digit of the current number
    let last = x % 10;

    if (last - 1 >= 0) {
        // Appending x-1 to the current number
        generateSteppingNos(x * 10 + last - 1);
    }

    // Appending x to the current number
    generateSteppingNos(x * 10 + last);

    if (last + 1 <= 9) {
        // Appending x+1 to the current number
        generateSteppingNos(x * 10 + last + 1);
    }
}

// Function to print N stepping numbers
function NSteppingNumbers(N) {
    // Set to store the stepping numbers
    let s = new Set();

    let arr = [10, 11, 12, 21, 22];

    // Generating stepping numbers
    for (let i = 1; i <= 9; i++) {
        generateSteppingNos(i);
        s.add(i);
    }

    for (let i = 0; i < arr.length; i++) {
        s.add(arr[i]);
    }

    let count = 1;

    // Printing N numbers from the set
    let ans = [];
    for (let it of s) {
        if (count <= N) {
            ans.push(it);
            count++;
        } else {
            break;
        }
    }
    console.log(ans.join(', '))
}

let N = 14;
NSteppingNumbers(N);

// This code is contributed by codebraxnzt

Output:

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 21, 22,

Program to print Even Odd Number Pyramid

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Program to print first N Stepping numbers

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