Smallest number by rearranging digits of a given number

Difficulty Level : Medium
Last Updated : 25 Mar, 2021

Find the Smallest number (Not leading Zeros) which can be obtained by rearranging the digits of given number.
Examples:

Input: n = 846903
Output: 304689

Input: n = 55010
Output: 10055

Steps to find the smallest number.

Count the frequency of each digit in the number.
Place the smallest digit (except 0) at the left most of required number.
and decrement the frequency of that digit by 1.
Place all remaining digits in ascending order from left to right.

This solution is based on counting sort.

C++

// C++ program for finding smallest number
// from digits of given number
#include<iostream>
using namespace std;
 
// function to find the smallest number
int smallest(int num)
{
    // initialize frequency of each digit to Zero
    int freq[10] = {0};
 
    // count frequency of each digit in the number
    while (num)
    {
        int d = num % 10; // extract last digit
        freq[d]++; // increment counting
        num = num / 10; //remove last digit
    }
 
    // Set the LEFTMOST digit to minimum expect 0
    int result = 0;
    for (int i = 1 ; i <= 9 ; i++)
    {
        if (freq[i])
        {
            result = i;
            freq[i]--;
            break;
        }
    }
 
    // arrange all remaining digits
    // in ascending order
    for (int i = 0 ; i <= 9 ; i++)
        while (freq[i]--)
            result = result * 10 + i;
 
    return result;
}
 
// Driver Program
int main()
{
    int num = 570107;
    cout << smallest(num);
    return 0;
}

Java

// Java program for finding smallest number
// from digits of given number
public class GFG {
 
    // function to find the smallest number
    static int smallest(int num)
    {
        // initialize frequency of each digit to Zero
        int[] freq = new int[10];
      
        // count frequency of each digit in the number
        while (num > 0)
        {
            int d = num % 10; // extract last digit
            freq[d]++; // increment counting
            num = num / 10; //remove last digit
        }
      
        // Set the LEFTMOST digit to minimum expect 0
        int result = 0;
        for (int i = 1 ; i <= 9 ; i++)
        {
            if (freq[i] != 0)
            {
                result = i;
                freq[i]--;
                break;
            }
        }
      
        // arrange all remaining digits
        // in ascending order
        for (int i = 0 ; i <= 9 ; i++)
            while (freq[i]-- != 0)
                result = result * 10 + i;
      
        return result;
    }
      
    // Driver Program
    public static void main(String args[])
    {
        int num = 570107;
        System.out.println(smallest(num));
    }
}
// This code is contributed by Sumit Ghosh

Python

# Function to find the smallest number
def smallest(lst):
     
    # Here i is index and n is the number of the list
    for i,n in enumerate(lst):
         
        # Checking for the first non-zero digit in the sorted list
        if n != '0':
             
            # Remove and store the digit from the lst
            tmp = lst.pop(i)
            break
     
    # Place the first non-zero digit at the starting
    # and return the final number
    return str(tmp) + ''.join(lst)
 
 
# Driver program
if __name__ == '__main__':
     
    # Converting the given numbers into string to form a list
    lst = list(str(570107))
    lst.sort()
     
    # Calling the function using the above list
    print smallest(lst)
     
# This code is contributed by Mahendra Yadav

C#

// C# program for finding smallest
// number from digits of given
// number
using System;
 
public class GFG {
 
    // function to find the smallest
    // number
    static int smallest(int num)
    {
         
        // initialize frequency of
        // each digit to Zero
        int[] freq = new int[10];
     
        // count frequency of each
        // digit in the number
        while (num > 0)
        {
             
            // extract last digit
            int d = num % 10;
             
            // increment counting
            freq[d]++;
             
            //remove last digit
            num = num / 10;
        }
     
        // Set the LEFTMOST digit to
        // minimum expect 0
        int result = 0;
        for (int i = 1 ; i <= 9 ; i++)
        {
            if (freq[i] != 0)
            {
                result = i;
                freq[i]--;
                break;
            }
        }
     
        // arrange all remaining digits
        // in ascending order
        for (int i = 0 ; i <= 9 ; i++)
            while (freq[i]-- != 0)
                result = result * 10 + i;
     
        return result;
    }
     
    // Driver Program
    public static void Main()
    {
        int num = 570107;
        Console.WriteLine(smallest(num));
    }
}
 
// This code is contributed by anuj_67.

PHP

<?php
// PHP program for finding smallest
// number from digits of given number
 
// function to find the smallest number
function smallest($num)
{
    // initialize frequency of
    // each digit to Zero
    $freq = array_fill(0, 10, 0);
 
    // count frequency of each
    // digit in the number
    while ($num)
    {
        $d = $num % 10; // extract last digit
        $freq[$d]++; // increment counting
        $num = (int)($num / 10); // remove last digit
    }
 
    // Set the LEFTMOST digit
    // to minimum expect 0
    $result = 0;
    for ($i = 1 ; $i <= 9 ; $i++)
    {
        if ($freq[$i])
        {
            $result = $i;
            $freq[$i]--;
            break;
        }
    }
 
    // arrange all remaining digits
    // in ascending order
    for ($i = 0 ; $i <= 9 ; $i++)
        while ($freq[$i] > 0)
        {
            $result = $result * 10 + $i;
            $freq[$i] -= 1;
        }
 
    return $result;
}
 
// Driver Code
$num = 570107;
echo smallest($num);
 
// This code is contributed by mits
?>

Javascript

<script>
 
// Javascript program for finding smallest number
// from digits of given number
 
// function to find the smallest number
function smallest(num)
{
    // initialize frequency of each digit to Zero
    var freq = Array(10).fill(0);
 
    // count frequency of each digit in the number
    while (num)
    {
        var d = num % 10; // extract last digit
        freq[d]++; // increment counting
        num = parseInt(num / 10); //remove last digit
    }
 
    // Set the LEFTMOST digit to minimum expect 0
    var result = 0;
    for (var i = 1 ; i <= 9 ; i++)
    {
        if (freq[i])
        {
            result = i;
            freq[i]--;
            break;
        }
    }
 
    // arrange all remaining digits
    // in ascending order
    for (var i = 0 ; i <= 9 ; i++)
        while (freq[i]--)
            result = result * 10 + i;
 
    return result;
}
 
// Driver Program
var num = 570107;
document.write(smallest(num));
 
// This code is contributed by rutvik_56.
</script>

Output:

Another Approach:Find smallest permutation of given number
This article is contributed by Ajay Kumar Agrahari(aJy aGr). If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
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