Sliding Window

Sliding window technique is primarily used to solve problems where we want to find the longest contiguous array satisfying a constraint.

When does it make sense?

The constraint is calculated by a function $f([a_i,a_{i+1},\dots ,a_j])$. The sliding window technique makes sense when calculating $f$ with addition of $a_{j+1}$ or removal of $a_i$ is easy knowing the value of $f([a_i,a_{i+1},\dots ,a_j])$.