# Maximum possible number with the given operation

Given a positive integer N, the task is to convert this integer to the maximum possible integer without leading zeroes by changing the digits. A digit X can only be changed into a digit Y if X + Y = 9.

Examples:

Input: N = 42
Output: 57
Change 4 -> 5 and 2 -> 7.

Input: N = 1
Output: 8

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: Only the digits which are greater than or equal to 5 need to be changed as changing the digits which are less than 5 will result in a larger number. After all the required digits have been updated, check whether the resultant number has a leading zero, if yes then change it to a 9.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach ` `#include ` `using` `namespace` `std; ` ` `  `// Function to return the maximum possible ` `// integer that can be obtained from the ` `// given integer after performing ` `// the given operations ` `string maxInt(string str) ` `{ ` `    ``// For every digit ` `    ``for` `(``int` `i = 0; i < str.length(); i++) { ` ` `  `        ``// Digits greater than or equal to 5 ` `        ``// need not to be changed as changing ` `        ``// them will lead to a smaller number ` `        ``if` `(str[i] < ``'5'``) { ` `            ``str[i] = (``'9'` `- str[i]) + ``'0'``; ` `        ``} ` `    ``} ` ` `  `    ``// The resulting integer ` `    ``// cannot have leading zero ` `    ``if` `(str[0] == ``'0'``) ` `        ``str[0] = ``'9'``; ` ` `  `    ``return` `str; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``string str = ``"42"``; ` ` `  `    ``cout << maxInt(str); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java implementation of the approach  ` `class` `GFG  ` `{ ` ` `  `    ``// Function to return the maximum possible  ` `    ``// integer that can be obtained from the  ` `    ``// given integer after performing  ` `    ``// the given operations  ` `    ``static` `String maxInt(``char` `str[])  ` `    ``{  ` `        ``// For every digit  ` `        ``for` `(``int` `i = ``0``; i < str.length; i++) ` `        ``{  ` `     `  `            ``// Digits greater than or equal to 5  ` `            ``// need not to be changed as changing  ` `            ``// them will lead to a smaller number  ` `            ``if` `(str[i] < ``'5'``) ` `            ``{  ` `                ``str[i] = (``char``)((``'9'` `- str[i]) + ``'0'``);  ` `            ``}  ` `        ``}  ` `     `  `        ``// The resulting integer  ` `        ``// cannot have leading zero  ` `        ``if` `(str[``0``] == ``'0'``)  ` `            ``str[``0``] = ``'9'``;  ` `     `  `        ``String str2 = ``new` `String(str); ` `        ``return` `str2;  ` `    ``}  ` `     `  `    ``// Driver code  ` `    ``public` `static` `void` `main (String[] args)  ` `    ``{  ` `        ``String str = ``"42"``;  ` `     `  `        ``System.out.println(maxInt(str.toCharArray()));  ` `    ``}  ` `} ` ` `  `// This code is contributed by AnkitRai01 `

## Python3

 `# Python3 implementation of the approach  ` ` `  `# Function to return the maximum possible  ` `# integer that can be obtained from the  ` `# given integer after performing  ` `# the given operations  ` `def` `maxInt(string):  ` `    ``string2 ``=` `"" ` `     `  `    ``# For every digit  ` `    ``for` `i ``in` `range``(``0``, ``len``(string)):  ` ` `  `        ``# Digits greater than or equal to 5  ` `        ``# need not to be changed as changing  ` `        ``# them will lead to a smaller number  ` `        ``if` `(string[i] < ``'5'``): ` `            ``string2 ``+``=` `str``((``ord``(``'9'``) ``-` `ord``(string[i]))) ` `        ``else``: ` `            ``string2 ``+``=` `str``(string[i]) ` `             `  `    ``# The resulting integer  ` `    ``# cannot have leading zero  ` `    ``if` `(string2[``0``] ``=``=` `'0'``):  ` `        ``string2[``0``] ``=` `'9'` ` `  `    ``return` `string2  ` ` `  `# Driver code  ` `if` `__name__ ``=``=` `'__main__'``:  ` ` `  `    ``string ``=` `"42"` `    ``print``(maxInt(string))  ` ` `  `# This code is contributed by ashutosh450 `

## C#

 `// C# implementation of the approach ` `using` `System;  ` ` `  `class` `GFG  ` `{ ` ` `  `    ``// Function to return the maximum possible  ` `    ``// integer that can be obtained from the  ` `    ``// given integer after performing  ` `    ``// the given operations  ` `    ``static` `String maxInt(``char` `[]str)  ` `    ``{  ` `        ``// For every digit  ` `        ``for` `(``int` `i = 0; i < str.Length; i++) ` `        ``{  ` `     `  `            ``// Digits greater than or equal to 5  ` `            ``// need not to be changed as changing  ` `            ``// them will lead to a smaller number  ` `            ``if` `(str[i] < ``'5'``) ` `            ``{  ` `                ``str[i] = (``char``)((``'9'` `- str[i]) + ``'0'``);  ` `            ``}  ` `        ``}  ` `     `  `        ``// The resulting integer  ` `        ``// cannot have leading zero  ` `        ``if` `(str[0] == ``'0'``)  ` `            ``str[0] = ``'9'``;  ` `     `  `        ``String str2 = ``new` `String(str); ` `        ``return` `str2;  ` `    ``}  ` `     `  `    ``// Driver code  ` `    ``public` `static` `void` `Main (String []args)  ` `    ``{  ` `        ``String str = ``"42"``;  ` `     `  `        ``Console.WriteLine(maxInt(str.ToCharArray()));  ` `    ``}  ` `} ` ` `  `// This code is contributed by Arnab Kundu `

Output:

```57
```

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