# Find Maximum number possible by doing at-most K swaps

Given a positive integer, find maximum integer possible by doing at-most K swap operations on its digits.

Examples:

```Input: M = 254, K = 1
Output: 524

Input: M = 254, K = 2
Output: 542

Input: M = 68543, K = 1
Output: 86543

Input: M = 7599, K = 2
Output: 9975

Input: M = 76543, K = 1
Output: 76543

Input: M = 129814999, K = 4
Output: 999984211
```

Idea is to consider every digit and swap it with digits following it one at a time and see if it leads to the maximum number. We repeat the process K times. The code can be further optimized if we swap only if current digit is less than the following digit.

Below is implementation of above idea –

## C++

 `// C++ program to find maximum integer possible by ` `// doing at-most K swap operations on its digits. ` `#include ` `using` `namespace` `std; ` ` `  `// function to find maximum integer possible by ` `// doing at-most K swap operations on its digits ` `void` `findMaximumNum(string str, ``int` `k, string& max) ` `{ ` `    ``// return if no swaps left ` `    ``if``(k == 0) ` `        ``return``; ` ` `  `    ``int` `n = str.length(); ` `     `  `    ``// consider every digit ` `    ``for` `(``int` `i = 0; i < n - 1; i++) ` `    ``{ ` `      `  `        ``// and compare it with all digits after it ` `        ``for` `(``int` `j = i + 1; j < n; j++) ` `        ``{ ` `            ``// if digit at position i is less than digit ` `            ``// at position j, swap it and check for maximum ` `            ``// number so far and recurse for remaining swaps ` `            ``if` `(str[i] < str[j]) ` `            ``{ ` `                ``// swap str[i] with str[j] ` `                ``swap(str[i], str[j]); ` ` `  `                ``// If current num is more than maximum so far ` `                ``if` `(str.compare(max) > 0) ` `                    ``max = str; ` ` `  `                ``// recurse of the other k - 1 swaps ` `                ``findMaximumNum(str, k - 1, max); ` ` `  `                ``// backtrack ` `                ``swap(str[i], str[j]); ` `            ``} ` `        ``} ` `    ``} ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``string str = ``"129814999"``; ` ` `  `    ``int` `k = 4; ` ` `  `    ``string max = str; ` `    ``findMaximumNum(str, k, max); ` ` `  `    ``cout << max << endl; ` ` `  `    ``return` `0; ` `} `

/div>

## Python3

# Python3 program to find maximum
# integer possible by doing at-most
# K swap operations on its digits.

# utility function to swap two
# characters of a string
def swap(string, i, j):

return (string[:i] + string[j] +
string[i + 1:j] +
string[i] + string[j + 1:])

# function to find maximum integer
# possible by doing at-most K swap
# operations on its digits
def findMaximumNum(string, k, maxm):

# return if no swaps left
if k == 0:
return

n = len(string)

# consider every digit
for i in range(n – 1):

# and compare it with all digits after it
for j in range(i + 1, n):

# if digit at position i is less than
# digit at position j, swap it and
# check for maximum number so far and
# recurse for remaining swaps
if string[i] < string[j]: # swap string[i] with string[j] string = swap(string, i, j) # If current num is more than # maximum so far if string > maxm:
maxm = string

# recurse of the other k – 1 swaps
findMaximumNum(string, k – 1, maxm)

# backtrack
string = swap(string, i, j)

# Driver Code
if __name__ == “__main__”:
string = “129814999”
k = 4
maxm = [string]
findMaximumNum(string, k, maxm)
print(maxm)

# This code is contributed
# by vibhu4agarwal

Output:

```999984211
```

The above code can further be optimized by stopping our search if all digits are already sorted in decreasing order. Please do share with us if you find more efficient ways to solve this problem.

Exercise :
1. Find minimum integer possible by doing at-least K swap operations on its digits.
2. Find maximum/minimum integer possible by doing exactly K swap operations on its digits.