Build a hash map from pairs
Updated
Building from two parallel lists means put a[i]→b[i] for each i. Later pairs with the same key overwrite earlier ones.
What to focus on
Keys [4,1,9] and values [2,8,3] become {4:2, 1:8, 9:3}. If a key repeats, the last value wins.
Worked examples
three pairs
a = [4, 1, 9], b = [2, 8, 3]- put in order
Result: {4:2, 1:8, 9:3}
repeat key
a = [4, 1, 4], b = [2, 8, 3]- 4→2 then 4→3 overwrites
Result: {4:3, 1:8}
empty
a = [], b = []- no puts
Result: {}
Try it
Write fromPairs(a, b). a is the list of keys. b is the list of values, same length. Put a[i]→b[i] in order. Last write wins for a repeated key. Return the map. a = [4, 1, 9], b = [2, 8, 3] → {4:2, 1:8, 9:3}. a = [4, 1, 4], b = [2, 8, 3] → {4:3, 1:8}. a = [], b = [] → {}.
a and b are equal-length lists of integers and may be empty.