Arrange given numbers to form the smallest number - GeeksforGeeks

30 Jun, 2021
Given an array arr[] of integer elements, the task is to arrange them in such a way that these numbers form the smallest possible number. For example, if the given array is {5, 6, 2, 9, 21, 1} then the arrangement will be 1212569.
Examples: 
Input: arr[] = {5, 6, 2, 9, 21, 1} Output: 1212569
Input: arr[] = {1, 2, 1, 12, 33, 211, 50} Output: 111221123350  
Approach: If all the given numbers are of at most one digit then the simple approach is sorting all numbers in ascending order. But if there is some number which have more than a single-digit then this approach will not work. Therefore, we have to sort the array by comparing any two elements in the following way: If the elements are A and B, then compare (A + B) with (B + A) where + represents concatenation.Below is the implementation of the above approach: 
C++
Java
Python3
C#
PHP
Javascript
// C++ implementation of the approach#include <algorithm>#include <iostream>using namespace std; // Utility function to print// the contents of an arrayvoid printArr(int arr[], int n){    for (int i = 0; i < n; i++)        cout << arr[i];} // A comparison function that return true// if 'AB' is smaller than 'BA' when// we concatenate two numbers 'A' and 'B'// For example, it will return true if// we pass 12 and 24 as arguments.// This function will be used by sort() functionbool compare(int num1, int num2){    // to_string function is predefined function    // to convert a number in string     // Convert first number to string format    string A = to_string(num1);     // Convert second number to string format    string B = to_string(num2);     // Check if 'AB' is smaller or 'BA'    // and return bool value since    // comparison operator '<=' returns    // true or false    return (A + B) <= (B + A);} // Function to print the arrangement// with the smallest valuevoid printSmallest(int N, int arr[]){    // If we pass the name of the comparison    // function it will sort the array    // according to the compare function    sort(arr, arr + N, compare);     // Print the sorted array    printArr(arr, N);} // Driver codeint main(){    int arr[] = { 5, 6, 2, 9, 21, 1 };    int N = sizeof(arr) / sizeof(arr[0]);    printSmallest(N, arr);     return 0;}
// Java implementation of the approachclass GFG{     // Utility function to print    // the contents of an array    public static void printArr(int[] arr, int n)    {        for (int i = 0; i < n; i++)            System.out.print(arr[i]);    }     // A comparison function that return negative    // if 'AB' is smaller than 'BA' when    // we concatenate two numbers 'A' and 'B'    // For example, it will return negative value if    // we pass 12 and 24 as arguments.    // This function will be used during sort    public static int compare(int num1, int num2)    {         // toString function is predefined function        // to convert a number in string         // Convert first number to string format        String A = Integer.toString(num1);         // Convert second number to string format        String B = Integer.toString(num2);                 // Check if 'AB' is smaller or 'BA'        // and return integer value        return (A+B).compareTo(B+A);    }     // Function to print the arrangement    // with the smallest value    public static void printSmallest(int N, int[] arr)    {         // Sort using compare function which        // is defined above        for (int i = 0; i < N; i++)        {            for (int j = i + 1; j < N; j++)            {                if (compare(arr[i], arr[j]) > 0)                {                    int temp = arr[i];                    arr[i] = arr[j];                    arr[j] = temp;                }            }        }         // Print the sorted array        printArr(arr, N);    }     // Driver code    public static void main(String[] args)    {        int[] arr = { 5, 6, 2, 9, 21, 1 };        int N = arr.length;        printSmallest(N, arr);    }} // This code is contributed by// sanjeev2552
# Python3 implementation of the approach # Utility function to print# the contents of an arraydef printArr(arr, n):     for i in range(0, n):        print(arr[i], end = "") # A comparison function that return true# if 'AB' is smaller than 'BA' when# we concatenate two numbers 'A' and 'B'# For example, it will return true if# we pass 12 and 24 as arguments.# This function will be used by sort() functiondef compare(num1, num2):     # Convert first number to string format    A = str(num1)     # Convert second number to string format    B = str(num2)     # Check if 'AB' is smaller or 'BA'    # and return bool value since    # comparison operator '<=' returns    # true or false    return int(A + B) <= int(B + A)     def sort(arr):         for i in range(len(arr)):        for j in range(i + 1, len(arr)):                         if compare(arr[i], arr[j]) == False:                arr[i], arr[j] = arr[j], arr[i] # Function to print the arrangement# with the smallest valuedef printSmallest(N, arr):     # If we pass the name of the comparison    # function it will sort the array    # according to the compare function    sort(arr)     # Print the sorted array    printArr(arr, N) # Driver codeif __name__ == "__main__":     arr = [5, 6, 2, 9, 21, 1]    N = len(arr)    printSmallest(N, arr) # This code is contributed by Rituraj Jain
// C# implementation for above approachusing System; class GFG{     // Utility function to print    // the contents of an array    public static void printArr(int[] arr, int n)    {        for (int i = 0; i < n; i++)            Console.Write(arr[i]);    }     // A comparison function that return negative    // if 'AB' is smaller than 'BA' when    // we concatenate two numbers 'A' and 'B'    // For example, it will return negative value if    // we pass 12 and 24 as arguments.    // This function will be used during sort    public static int compare(int num1, int num2)    {         // toString function is predefined function        // to convert a number in string         // Convert first number to string format        String A = num1.ToString();         // Convert second number to string format        String B = num2.ToString();                 // Check if 'AB' is smaller or 'BA'        // and return integer value        return (A+B).CompareTo(B+A);    }     // Function to print the arrangement    // with the smallest value    public static void printSmallest(int N, int[] arr)    {         // Sort using compare function which        // is defined above        for (int i = 0; i < N; i++)        {            for (int j = i + 1; j < N; j++)            {                if (compare(arr[i], arr[j]) > 0)                {                    int temp = arr[i];                    arr[i] = arr[j];                    arr[j] = temp;                }            }        }         // Print the sorted array        printArr(arr, N);    }     // Driver code    public static void Main(String[] args)    {        int[] arr = { 5, 6, 2, 9, 21, 1 };        int N = arr.Length;        printSmallest(N, arr);    }} // This code is contributed by Rajput-Ji
<?php// PHP implementation of the approach // Utility function to print// the contents of an arrayfunction printArr($arr, $n){    for ($i = 0; $i < $n; $i++)        echo $arr[$i];} // A comparison function that return true// if 'AB' is smaller than 'BA' when// we concatenate two numbers 'A' and 'B'// For example, it will return true if// we pass 12 and 24 as arguments.// This function will be used by sort() functionfunction compare($num1, $num2){    // to_string function is predefined function    // to convert a number in string     // Convert first number to string format    $A = (string)$num1 ;     // Convert second number to string format    $B = (string)$num2 ;     // Check if 'AB' is smaller or 'BA'    // and return bool value since    // comparison operator '<=' returns    // true or false    if((int)($A . $B) <= (int)($B . $A))    {        return true;    }    else        return false;}  function sort_arr($arr){         for ($i = 0; $i < count($arr) ; $i++)    {        for ($j = $i + 1;$j < count($arr) ; $j++)        {            if (compare($arr[$i], $arr[$j]) == false)            {                $temp = $arr[$i] ;                $arr[$i] = $arr[$j] ;                $arr[$j] = $temp ;            }        }    }        return $arr ;    } // Function to print the arrangement// with the smallest valuefunction printSmallest($N, $arr){    // If we pass the name of the comparison    // function it will sort the array    // according to the compare function    $arr = sort_arr($arr);     // Print the sorted array    printArr($arr, $N);}     // Driver code    $arr = array(5, 6, 2, 9, 21, 1 );    $N = count($arr);    printSmallest($N, $arr);     // This code is contributed by Ryuga ?>
<script>    // Javascript implementation of the approach     // Utility function to print    // the contents of an array    function printArr(arr,n)    {        for (let i = 0; i < n; i++)            document.write(arr[i]);    }     // A comparison function that return true    // if 'AB' is smaller than 'BA' when    // we concatenate two numbers 'A' and 'B'    // For example, it will return true if    // we pass 12 and 24 as arguments.    // This function will be used by sort() function    function compare(num1,num2)    {        // to_string function is predefined function        // to convert a number in string         // Convert first number to string format        let A = num1.toString();         // Convert second number to string format        let B = num2.toString();         // Check if 'AB' is smaller or 'BA'        // and return bool value since        // comparison operator '<=' returns        // true or false        return (A + B).localeCompare(B + A);    }     // Function to print the arrangement    // with the smallest value    function printSmallest(N,arr)    {        // If we pass the name of the comparison        // function it will sort the array        // according to the compare function        // Sort using compare function which        // is defined above        for (let i = 0; i < N; i++)        {            for (let j = i + 1; j < N; j++)            {                if (compare(arr[i], arr[j]) > 0)                {                    let temp = arr[i];                    arr[i] = arr[j];                    arr[j] = temp;                }            }        }         // Print the sorted array        printArr(arr,N);    }     // Driver code     let arr = [ 5, 6, 2, 9, 21, 1 ];    let N = arr.length;    printSmallest(N,arr);</script>
1212569
 
rituraj_jain
ankthon
sanjeev2552
Rajput-Ji
sai bhargava ramu
vaibhavrabadiya117
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