# Find the largest number that can be formed by changing at most K digits

Given a string str representing a number and an integer K, the task is to find the largest number that can be formed by changing at most K digits in the given number.

Examples:

Input: str = “569431”, K = 3
Output: 999931
Replace first, second and fourth digits with 9.

Input: str = “5687”, K = 2
Output: 9987

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

Approach: In order to get the maximum number possible, leftmost digits must be replaced with 9s. For every digit of the number starting from the leftmost digit, if it is not already 9 and K is greater than 0 then replace it with 9 and decrement K by 1. Repeat these steps for every digit while K is greater than 0. Finally, print the updated number.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach ` `#include ` `using` `namespace` `std; ` ` `  `// Function to return the maximum number ` `// that can be formed by changing ` `// at most k digits in str ` `string findMaximumNum(string str, ``int` `n, ``int` `k) ` `{ ` ` `  `    ``// For every digit of the number ` `    ``for` `(``int` `i = 0; i < n; i++) { ` ` `  `        ``// If no more digits can be replaced ` `        ``if` `(k < 1) ` `            ``break``; ` ` `  `        ``// If current digit is not already 9 ` `        ``if` `(str[i] != ``'9'``) { ` ` `  `            ``// Replace it with 9 ` `            ``str[i] = ``'9'``; ` ` `  `            ``// One digit has been used ` `            ``k--; ` `        ``} ` `    ``} ` ` `  `    ``return` `str; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``string str = ``"569431"``; ` `    ``int` `n = str.length(); ` `    ``int` `k = 3; ` ` `  `    ``cout << findMaximumNum(str, n, k); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java implementation of the approach ` `class` `GFG ` `{ ` `    ``// Function to return the maximum number ` `    ``// that can be formed by changing ` `    ``// at most k digits in str ` `    ``static` `StringBuilder findMaximumNum(StringBuilder str,  ` `                                             ``int` `n, ``int` `k) ` `    ``{ ` `     `  `        ``// For every digit of the number ` `        ``for` `(``int` `i = ``0``; i < n; i++)  ` `        ``{ ` `     `  `            ``// If no more digits can be replaced ` `            ``if` `(k < ``1``) ` `                ``break``; ` `     `  `            ``// If current digit is not already 9 ` `            ``if` `(str.charAt(i) != ``'9'``)  ` `            ``{ ` `     `  `                ``// Replace it with 9 ` `                ``str.setCharAt(i, ``'9'``); ` `     `  `                ``// One digit has been used ` `                ``k--; ` `            ``} ` `        ``} ` `        ``return` `str; ` `    ``} ` `     `  `    ``// Driver code ` `    ``public` `static` `void` `main (String [] args) ` `    ``{ ` `        ``StringBuilder str = ``new` `StringBuilder(``"569431"``); ` `         `  `        ``int` `n = str.length(); ` `        ``int` `k = ``3``; ` `     `  `        ``System.out.println(findMaximumNum(str, n, k)); ` `    ``} ` `} ` ` `  `// This code is contributed by ihritik `

## Python3

 `# Python3 implementation of the approach  ` ` `  `# Function to return the maximum number  ` `# that can be formed by changing  ` `# at most k digits in str  ` `def` `findMaximumNum(st, n, k): ` ` `  `    ``# For every digit of the number  ` `    ``for` `i ``in` `range``(n):  ` ` `  `        ``# If no more digits can be replaced  ` `        ``if` `(k < ``1``):  ` `            ``break` ` `  `        ``# If current digit is not already 9  ` `        ``if` `(st[i] !``=` `'9'``):  ` ` `  `            ``# Replace it with 9  ` `            ``st ``=` `st[``0``:i] ``+` `'9'` `+` `st[i ``+` `1``:]  ` ` `  `            ``# One digit has been used  ` `            ``k ``-``=` `1` ` `  `    ``return` `st ` ` `  `# Driver code  ` `st ``=` `"569431"` `n ``=` `len``(st)  ` `k ``=` `3` `print``(findMaximumNum(st, n, k)) ` ` `  `# This code is contributed by ` `# divyamohan123 `

## C#

 `// C# implementation of the approach ` `using` `System; ` `using` `System.Text; ` ` `  `class` `GFG ` `{ ` `    ``// Function to return the maximum number ` `    ``// that can be formed by changing ` `    ``// at most k digits in str ` `    ``static` `StringBuilder findMaximumNum(StringBuilder str,  ` `                                        ``int` `n, ``int` `k) ` `    ``{ ` `     `  `        ``// For every digit of the number ` `        ``for` `(``int` `i = 0; i < n; i++)  ` `        ``{ ` `     `  `            ``// If no more digits can be replaced ` `            ``if` `(k < 1) ` `                ``break``; ` `     `  `            ``// If current digit is not already 9 ` `            ``if` `(str[i] != ``'9'``) ` `            ``{ ` `     `  `                ``// Replace it with 9 ` `                ``str[i] = ``'9'``; ` `     `  `                ``// One digit has been used ` `                ``k--; ` `            ``} ` `        ``} ` `        ``return` `str; ` `    ``} ` `     `  `    ``// Driver code ` `    ``public` `static` `void` `Main () ` `    ``{ ` `        ``StringBuilder str = ``new` `StringBuilder(``"569431"``); ` `         `  `        ``int` `n = str.Length; ` `        ``int` `k = 3; ` `     `  `        ``Console.WriteLine(findMaximumNum(str, n, k)); ` `    ``} ` `} ` ` `  `// This code is contributed by ihritik `

Output:

```999931
```

My Personal Notes arrow_drop_up Check out this Author's contributed articles.

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.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.

Improved By : ihritik, divyamohan123

Article Tags :
Practice Tags :

Be the First to upvote.

Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.