It is faster , but less space efficient .

The thing is - you cannot determine even an approximate size of the resulting vector beforehand .

Sure , the input {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16} requires the output vector to have a size equal to 16 elements .

And input {1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8} requires the output vector to have a size equal to 8 elements .

While input {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} requires the output vector to have a size equal to just only 1 element .

Favoring speed over space is generally a good idea , but i think it is also worth knowing when "reserve" can be used with/without drawbacks .

This code is good short and straight to the point. My only question is what does the #include algorithm> #include iterator> and #include unordered_set> do for this code?

Goot solution but why we need #include <unordered_set> here?

You could also call the member function "reserve" on the result vector before doing the unique_copy algorithm. This would mean one heap allocation instead of an unknown number of allocations as the vector grows in size.

You can have a print satement in the begining of your function with all your input data

This test is invalid
There's mentioned: the number of pronouns provided will be equal to the number of Noun Phrases in the sentence
but i get:

'adj adj word adj aux adj word aux aux aux aux adj aux adj aux word n aux adj aux n adj n adj adj word aux adj word n n adj word n adj adj word adj aux n adj aux adj adj adj n adj n n aux aux aux aux n n',
[ '0', '1', '2', '3' ],
{ n: 'N', aux: 'aux', adj: 'adj' }

where number of n is 12 and only 4 pronouns;
Language: js

Tere's something wierd going on with this array joining and ';' in the end
probably should be joined
not like this: "Buy: 263 Sell: 11802; Badly formed 2: CLH16.NYM 50 56 S ;OWW 1000 11 S ;"
but like this: "Buy: 263 Sell: 11802; Badly formed 2: CLH16.NYM 50 56 S; OWW 1000 11 S"

HAHAHHAHAHHA LOL