Priority queue 2

#1

how do we know a.dist() > b.dist () is giving nearer car…i am confused about working of > and < signs …

#2

Lets talk in case of integers rather than this specific case. Lets say our comparator is:

void operator()(int a,int b){
     return (a<b);
}

Always perceive the return value of the comparator as answer to the question:

Can ‘a’ come before ‘b’ ?

So, in the comparator above, if we ask this question, it will return “true” iff (a<b). This means that if (a<b), ‘a’ can come before ‘b’ . So, if you were using this comparator for ‘sort’ function (in STL), in the final (sorted) array, ‘a’ will appear before ‘b’ if (a<b).(You can extend this logic for each pair of numbers and conclude that array will be sorted in ascending order).

Similarly if you were to use this comparator for priority_queue (in STL), format the question to:

Can ‘a’ come below ‘b’ ?

So, in the case of above comparator, ‘a’ can come below ‘b’ iff (a<b), which means, if a<b, then ‘a’ will go below (in priority_queue) and ‘b’ will go on top. So the top element will always be greater than those below it (aka max_heap).

So, back to your doubt,

return a.dist()>b.dist();

is giving nearest car because if a.dist()>b.dist(), Car ‘a’ can go below Car ‘b’, thus the Car on the top will have lesser distance than the Car(s) below it (aka min_heap).

Comparater function
Sort function working
#3

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