Minimum Skill-Covering Window
`log` is a string of single-character skill codes practiced each minute, in order. `required` lists the skill codes you still need to cover (a code can repeat if you need it more than once). Return the SHORTEST contiguous slice of `log` that contains every code in `required` at least as many times a
`log` is a string of single-character skill codes practiced each minute, in order. `required` lists the skill codes you still need to cover (a code can repeat if you need it more than once). Return the SHORTEST contiguous slice of `log` that contains every code in `required` at least as many times a
