How does the minimum window substring problem use the sliding window?

Expand the right pointer until the window contains all characters from the target string, tracked by comparing character frequency maps. Once valid, try to shrink from the left while maintaining validity, updating the minimum valid window found. When shrinking makes the window invalid, resume expanding right. Use a counter tracking how many target characters are satisfied to determine validity in O of one rather than comparing full frequency maps each time. The overall time is O of n plus m where n is the source string length and m is the target length.