Thanks for spending time to view this !
Btw currently Iam learning graph theory (beginner). But i am struggling in storing the graph like, if the edges given are from 0, 1, 2, 3, 4… through N then i will be storing it in O(1) by direcctly accessing the i th index.

graph[0] -> 1 -> 2 -> 3
graph[1] -> 0 -> 3 -> 4

and so on…

But what if i get vertices like A,B,C,D … or something like 21, 35, 67, 89 (just for example). In such cases how can i access the index of those big valued vertices or in case of characters how can i even store it in ADJACENCY LIST.
0 → graph[A] → B → C
1 → graph[B] → A → D
how???

If there are bigger numbers, you can use map. Not only for Large numbers, map can be used for any data types the language supports. Think about some real-life situation: Cities are nodes and the roads are edges. You can still use map in CPP and Java or dict in Python.