I just completed Disjoint set in the graph explore card, other than that all the others seem locked.
Are these open to premium users or they are in progress and will be unlocked later at some point in time. Can anybody either of them ?

There is a past thread refering to this below which refers to the same
https://leetcode.com/discuss/explore/graph/1812748/When-I-can-access-the-%22The-Depth-First-Search-Algorithm-in-Graph%22