Helpful Maths - Algorithm

Here's your approach:

$1.$ Read the input string.

$2.$ Create an empty vector to store digits.

$3.$ Loop through each character in the string.

$4.$ If the character is a digit, add it to the vector.

$5.$ Sort the vector using sort().

$6.$ Print the first digit.

$7.$ For each remaining digit, print a plus sign followed by the digit.

$8.$ Done. The solution uses filtering, sorting, and formatted output. You separate concerns: first extract digits, then sort them, then format the result. Each step is simple on its own.