Theoretically, It means, If u r having a stack of Size N, then it will contain N most recently used page entries. Consider the same set of Entries, but this time use stack of N+1 size. If you compare, top N entries of both stack, they will be Same.
Consider this Example:-
String: 4 7 0 7 1 0 1 2 3
Stack 1 of size 4 -> 3, 2, 1, 0 (They are the most recently used, 3 is at top of stack because it arrived that, means most recent)
stack 2 of size 5 -> 3, 2, 1,0,7 (Here 7 is there but at the last entry)
Let's implement this Stack,
Initially Empty:
read 4
Stack-> 4
reading 7
Stack-> 7 4
Read 0
Stack -> 0 7 4
Read 7
Stack -> 7 0 7 4 (Remove duplicate from bottom) => 7 0 4
Read 1
Stack -> 1 7 0 4
Read 0
Stack -> 0 1 7 4 (You know what happened here)
Read 1 -> 1 0 7 4
read 2 -> 2 1 0 7
read 3 -> 3 2 1 0 (Final State)
For Stack of size 5, final value will be -> 3 2 1 0 7
Now compare top 4 entries of both stack:- they are same ie., 3 2 1 0
