How to successfully erase multiple characters from a string in inner loop !!

 The expression i = max(-1LL, i - 2); is used to adjust the index i after removing two characters from the string and ensure that i does not become less than -1. Here’s what each part means:

Breakdown:

1. i - 2:

   • After erasing two characters from the string at position i, we move the index back by 2 to account for the removed characters.
   • This is necessary because, after removing characters, we need to re-check the new characters that come into the current and previous positions.

2. -1LL:

   • This represents the value -1 as a long long data type (LL suffix means "long long").
   • The use of -1 here is to ensure that after the adjustment, the index i doesn't become negative and out of bounds for the loop. Specifically, if we subtract 2 from a very low index (like i = 0 or i = 1), i - 2 would result in a negative value like -1 or lower.
   • By limiting i to -1 at most, we prevent potential issues with indexing (e.g., accessing an invalid string position).

3. max(-1LL, i - 2):

   • The max function returns the larger of the two values: -1LL and i - 2.
   • This ensures that i never goes below -1. If i - 2 is less than -1, it will return -1, otherwise, it will return i - 2.

Why Use max(-1LL, i - 2):

• After erasing two characters, we move the index back to ensure we don't miss checking new adjacent characters.
• The max ensures that i does not go out of bounds, particularly when i is close to the beginning of the string. If i goes below -1, it might cause invalid indexing in subsequent iterations.

Example:

Suppose i = 1 before erasing two characters:

• i - 2 would be -1.
• The max(-1LL, -1) returns -1.
• This ensures that i is not set to a value lower than -1, which could potentially cause errors.

In this case, setting i = -1 means that the next iteration will set i = 0 (since i++ happens at the end of the loop), so no character is skipped.

This is mainly a safeguard to prevent i from going negative in a way that would break the program.

If you want to delete 3 chars then it will be i = max(-1ll,i-3)