LeetCode 992 Subarrays with K Different Integers (滑动窗 推荐)
Givenanintegerarraynumsandanintegerk,returnthenumberofgoodsubarraysofnums.Agoodarrayisanarraywherethenumberofdifferentintegersinthatarrayisexactlyk.Forexample,[1,2,3,1,2]has3differentintegers:1,2,and3