Compare saved lists: overlap and difference

After building the two ID lists, we can find their common members without scanning every original field again. For each May ID x, compare it with each Chennai ID y. On equality, append x to the result.

Common = []
foreach x in MayIDs:
    foreach y in ChennaiIDs:
        if x == y:
            Common = Common ++ [x]

There are 4 × 8 = 32 equality tests in this complete nested scan. We do not divide by two: these are comparisons across two lists, not unordered pairs within one list. Because each input here has unique IDs, the result contains each common student once.

With duplicates, raw nested matching can repeat results: [3,3] matched with [3,3] appends 3 four times. To implement set-style intersection, require unique inputs or add “if NOT member(Common,x)” before appending. Specify which meaning you want.

Find May students who are not in Chennai #

MayOnly = []
foreach x in MayIDs:
    if NOT member(ChennaiIDs, x):
        MayOnly = MayOnly ++ [x]
# [13,23]: Gopi and Deepika

Absence requires checking the whole other list unless a match is found first. Appending x whenever x != y is wrong: almost every ID differs from some y, including IDs that are also present. Union is another set-like operation: begin with one unique list, then append only members of the other list not already present.