# Maximize a number considering permutations with values smaller than limit

• Difficulty Level : Easy
• Last Updated : 02 Aug, 2022

Given two numbers N and M. Construct maximal number by permuting (changing order) the digits of N, not exceeding M.

Note: It is allowed to leave N as it is.

Examples:

Input : N = 123, M = 222
Output : 213
There are total 3! permutations possible for N = 123, But the only permutation that satisfies the given condition is 213. Similarly, In example 2, there are total 4! permutations possible for N = 3921, But the only permutation that satisfies the given condition is 9321.
Input : N = 3921, M = 10000
Output : 9321

Approach: Let’s construct the answer digit by digit starting from the leftmost. We are asked to build a lexicographically maximal answer. So in this order, we should choose the greatest digit on each step. The approach is to iterate over all possible digits starting from the greatest. For each digit check if it’s possible to put it in this position and compare the resulting number with the number M. If it comes less than or equal to the value of M, then proceed to the next digit.

Below is the CPP implementation of the above approach:

## CPP

 `// CPP program to Maximize the given number.` `#include `   `using` `namespace` `std;`   `// Function to maximize the number N with` `// limit as M.` `string maximizeNumber(string N, ``int` `M)` `{` `    ``// Sorting the digits of the` `    ``// number in increasing order.` `    ``sort(N.begin(), N.end());`   `    ``for` `(``int` `i = 0; i < N.size(); i++) {` `        ``for` `(``int` `j = i + 1; j < N.size(); j++) {`   `            ``// Copying the string into another` `            ``// temp string.` `            ``string t = N;`   `            ``// Swapping the j-th char(digit)` `            ``// with i-th char(digit)` `            ``swap(t[j], t[i]);`   `            ``// Sorting the temp string` `            ``// from i-th pos to end.` `            ``sort(t.begin() + i + 1, t.end());`   `            ``// Checking if the string t is` `            ``// greater than string N and less` `            ``// than or equal to the number M.` `            ``if` `(stoll(t) > stoll(N) && stoll(t) <= M)`   `                ``// If yes then, we will permanently` `                ``// swap the i-th char(or digit)` `                ``// with j-th char(digit).` `                ``swap(N[i], N[j]);` `        ``}` `    ``}`   `    ``// Returns the maximized number.` `    ``return` `N;` `}`   `// Driver function` `int` `main()` `{` `    ``string N = ``"123"``;` `    ``int` `M = 222;` `    ``cout << maximizeNumber(N, M);` `    ``return` `0;` `}` `// This code is contributed by KaaL-EL.`

## Java

 `/*package whatever //do not write package name here */`   `import` `java.io.*;` `import` `java.util.Arrays;`   `class` `GFG {` `    ``// Java has no built-in swap function.` `    ``public` `static` `String swap(String str, ``int` `i, ``int` `j)` `    ``{` `        ``char` `ch[] = str.toCharArray();` `        ``char` `temp = ch[i];` `        ``ch[i] = ch[j];` `        ``ch[j] = temp;` `        ``return` `new` `String(ch);` `    ``}`   `    ``// Since STRINGS are immutable in Java, first we have to` `    ``// convert it to a character array in order to sort.` `    ``public` `static` `String` `    ``sortString(String string, ``int` `s_index, ``int` `e_index)` `    ``{` `        ``char` `tempArray[] = string.toCharArray();` `        ``// Sorting temp array using` `        ``Arrays.sort(tempArray, s_index, e_index);` `        ``// returning the new sorted string` `        ``return` `new` `String(tempArray);` `    ``}`   `    ``public` `static` `String maximizeNumber(String N, ``int` `M)` `    ``{` `        ``// Sorting the digits of the` `        ``// number in increasing order.` `        ``N = sortString(N, ``0``, N.length());`   `        ``for` `(``int` `i = ``0``; i < N.length(); i++) {` `            ``for` `(``int` `j = i + ``1``; j < N.length(); j++) {`   `                ``// Copying the string into another` `                ``// temp string.` `                ``String t = N;`   `                ``// Swapping the j-th char(digit)` `                ``// with i-th char(digit)` `                ``t = swap(t, j, i);`   `                ``// Sorting the temp string` `                ``// from i-th pos to end.` `                ``t = sortString(t, i + ``1``, t.length());`   `                ``// Checking if the string t is` `                ``// greater than string N and less` `                ``// than or equal to the number M.` `                ``if` `(Long.parseLong(t) > Long.parseLong(N)` `                    ``&& Long.parseLong(t) <= M)`   `                    ``// If yes then, we will permanently` `                    ``// swap the i-th char(or digit)` `                    ``// with j-th char(digit).` `                    ``N = swap(N, i, j);` `            ``}` `        ``}`   `        ``// Returns the maximized number.` `        ``return` `N;` `    ``}`   `    ``// Driver Code` `    ``public` `static` `void` `main(String[] args)` `    ``{` `        ``String N = ``"123"``;` `        ``int` `M = ``222``;` `        ``System.out.println(maximizeNumber(N, M));` `    ``}` `}` `//This code is contributed by KaaL-EL.`

## Python3

 `# Python3 program to implement the approach`   `# Python3 has no built-in swap function.` `def` `swap(``str``, i, j):` `    ``ch ``=` `list``(``str``)` `    ``temp ``=` `ch[i]` `    ``ch[i] ``=` `ch[j]` `    ``ch[j] ``=` `temp` `    ``return` `"".join(ch)`   `# Since STRINGS are immutable in JavaScript, first we have` `# to convert it to a character array in order to sort.` `def` `sortString(``str``, s_index, e_index):` `    ``tempArray ``=` `list``(``str``)`   `    ``# Sorting temp array using` `    ``tempArray ``=` `tempArray[:s_index] ``+` `sorted``(tempArray[s_index: e_index])`   `    ``# returning the new sorted string` `    ``return` `"".join(tempArray)`   `def` `maximizeNumber(N, M):` `    ``# Sorting the digits of the` `    ``# number in increasing order.` `    ``N ``=` `sortString(N, ``0``, ``len``(N))`   `    ``for` `i ``in` `range``(``len``(N)):` `        ``for` `j ``in` `range``(i ``+` `1``, ``len``(N)):`   `            ``# Copying the string into another` `            ``# temp string.` `            ``t ``=` `N`   `            ``# Swapping the j-th char(digit)` `            ``# with i-th char(digit)`   `            ``t ``=` `swap(t, j, i)`   `            ``# Sorting the temp string` `            ``# from i-th pos to end.` `            ``t ``=` `sortString(t, i ``+` `1``, ``len``(t))`   `            ``# Checking if the string t is` `            ``# greater than string N and less` `            ``# than or equal to the number M.` `            ``if` `(``int``(t) > ``int``(N) ``and` `int``(t) <``=` `M):`   `                ``# If yes then, we will permanently` `                ``# swap the i-th char(or digit)` `                ``# with j-th char(digit).` `                ``N ``=` `swap(N, i, j)`   `    ``# Returns the maximized number.` `    ``return` `N`   `# Driver Code` `N ``=` `"123"` `M ``=` `222` `print``(maximizeNumber(N, M))`   `# This code is contributed by phasing17`

## C#

 `// C# program to implement the approach`   `using` `System;` `using` `System.Collections.Generic;`   `class` `GFG {`   `    ``// C# has no built-in swap function.` `    ``public` `static` `string` `swap(String str, ``int` `i, ``int` `j)` `    ``{` `        ``char``[] ch = str.ToCharArray();` `        ``char` `temp = ch[i];` `        ``ch[i] = ch[j];` `        ``ch[j] = temp;` `        ``return` `new` `string``(ch);` `    ``}`   `    ``// Since STRINGS are immutable in C#, first we have to` `    ``// convert it to a character array in order to sort.` `    ``public` `static` `string` `sortString(``string` `str, ``int` `s_index,` `                                    ``int` `e_index)` `    ``{` `        ``char``[] tempArray = str.ToCharArray();` `        ``// Sorting temp array using` `        ``Array.Sort(tempArray, s_index, e_index - s_index);` `        ``// returning the new sorted string` `        ``return` `new` `string``(tempArray);` `    ``}`   `    ``public` `static` `string` `maximizeNumber(``string` `N, ``int` `M)` `    ``{` `        ``// Sorting the digits of the` `        ``// number in increasing order.` `        ``N = sortString(N, 0, N.Length);`   `        ``for` `(``int` `i = 0; i < N.Length; i++) {` `            ``for` `(``int` `j = i + 1; j < N.Length; j++) {`   `                ``// Copying the string into another` `                ``// temp string.` `                ``string` `t = N;`   `                ``// Swapping the j-th char(digit)` `                ``// with i-th char(digit)` `                ``t = swap(t, j, i);`   `                ``// Sorting the temp string` `                ``// from i-th pos to end.` `                ``t = sortString(t, i + 1, t.Length);`   `                ``// Checking if the string t is` `                ``// greater than string N and less` `                ``// than or equal to the number M.` `                ``if` `(Convert.ToInt64(t) > Convert.ToInt64(N)` `                    ``&& Convert.ToInt64(t) <= M)`   `                    ``// If yes then, we will permanently` `                    ``// swap the i-th char(or digit)` `                    ``// with j-th char(digit).` `                    ``N = swap(N, i, j);` `            ``}` `        ``}`   `        ``// Returns the maximized number.` `        ``return` `N;` `    ``}`   `    ``// Driver Code` `    ``public` `static` `void` `Main(``string``[] args)` `    ``{` `        ``string` `N = ``"123"``;` `        ``int` `M = 222;` `        ``Console.WriteLine(maximizeNumber(N, M));` `    ``}` `}`   `// This code is contributed by phasing17`

## Javascript

 `// JavaScript program to implement the approach`   `// JavaScript has no built-in swap function.` `function` `swap(str, i, j)` `{` `    ``let ch = str.split(``""``);` `    ``let temp = ch[i];` `    ``ch[i] = ch[j];` `    ``ch[j] = temp;` `    ``return` `ch.join(``""``);` `}`   `// Since STRINGS are immutable in JavaScript, first we have` `// to convert it to a character array in order to sort.` `function` `sortString(str, s_index, e_index)` `{` `    ``let tempArray = str.split(``""``);` `    ``// Sorting temp array using` `    ``tempArray` `        ``= tempArray.slice(0, s_index)` `              ``.concat(` `                  ``tempArray.slice(s_index, e_index).sort());`   `    ``// returning the new sorted string` `    ``return` `tempArray.join(``""``);` `}`   `function` `maximizeNumber(N, M)` `{` `    ``// Sorting the digits of the` `    ``// number in increasing order.` `    ``N = sortString(N, 0, N.length);`   `    ``for` `(``var` `i = 0; i < N.length; i++) {` `        ``for` `(``var` `j = i + 1; j < N.length; j++) {`   `            ``// Copying the string into another` `            ``// temp string.` `            ``let t = N;`   `            ``// Swapping the j-th char(digit)` `            ``// with i-th char(digit)`   `            ``t = swap(t, j, i);`   `            ``// Sorting the temp string` `            ``// from i-th pos to end.` `            ``t = sortString(t, i + 1, t.length);`   `            ``// Checking if the string t is` `            ``// greater than string N and less` `            ``// than or equal to the number M.` `            ``if` `(parseInt(t) > parseInt(N)` `                ``&& parseInt(t) <= M)`   `                ``// If yes then, we will permanently` `                ``// swap the i-th char(or digit)` `                ``// with j-th char(digit).` `                ``N = swap(N, i, j);` `        ``}` `    ``}`   `    ``// Returns the maximized number.` `    ``return` `N;` `}`   `// Driver Code` `let N = ``"123"``;` `let M = 222;` `console.log(maximizeNumber(N, M));`   `// This code is contributed by phasing17`

Output

`213`

Time complexity : O(n3 log n)
Auxiliary Space: O(n),  since n extra space has been taken.

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