problem statement $($you should use only iostream and string header files.$)$

You are given a string consisting of English uppercase and lowercase letters and decimal

numbers. You can create a strictly increasing sequence $($SIS$)$ by picking each letter from

the beginning of this string one by one. And this sequence consists of the numbers $0$ to $9,$

lowercase English letters a to z$,$ and uppercase English letters A to Z in order. If you receive

$2648$ as input, SIS can be satisfied with just single$-$digit strings like $\{2\},\{4\},\{6\},\{8\}.$ And

it also satisfied with two$-$digit strings like $\{2,6\},\{2,4\},\{2,8\},\{6,8\},$ and three$-$digit strings

like $\{2,6,8\},\{2,4,8\}.$ However, strings like $\{2,6,4,8\}$ cannot satisfy SIS because $4$ is less

than $6.$

$1$

Your goal is to find the length of the longest string that satisfies SIS for a given string.

In the case above, your code should print $3$ because the longest string that satisfies SIS is $3$

characters long. For example, if you receive $1234$abcABC$$ as input, all strings will increase

in order from the beginning, and the result should be $10.$

Note that consecutive numbers or letters are considered one sequence. For example, input like $00001$

should be calculated as $\{0,1\}$ and printed $2.$ Even if the result is the same,

there may be various cases that satisfy the longest SIS. The maximum value of the result

that can be printed will be $09(10)+$ a $$ z$(26)+$ A $$ Z$(26)=62.$

Students can use recursion function in this problem. A recursive function is a function

that solves a problem by calling itself. Functions break a problem into smaller problems and

solve those smaller problems in the same way. This process is repeated until the simplest

form of the problem, i$.$e$.$ the base case, is reached. The following code is a function that

calculates the factorial with recursive function.