On what principle do you increase or decrease the have counter?

In Go (Golang), the counter have is often used in algorithms related to counting or tracking the number of unique elements, for example, in sliding window problems.

The principle of changing the have counter is as follows:

• Increase have when a new unique element that meets the problem's condition is added (for example, an element from the target set).
• Decrease have when an element is removed, and its count in the current window becomes less than required (for example, less than in the reference set).

In other words, have reflects the number of unique elements that currently satisfy the condition. Its increase and decrease occur when the window or state changes, to track when the desired state is reached or lost.

Example: in the problem of finding the minimum subarray containing all characters of string t, have increases when a character is added that was not fully covered before, and decreases when a character is removed, breaking the coverage.