A sliding window is an abstract concept commonly used in array/string problems. A window is a range of elements in the array/string which usually defined by the start and end indices, i.e. [i, j) (left-closed, right-open). A sliding window is a window “slides” its two boundaries to the certain direction. For example, if we slide [i, j) to the right by 1 element, then it becomes [i+1, j+1) (left-closed, right-open).
