Syntax:
#include <algorithm> bool is_heap(iterator start, iterator end); bool is_heap(iterator start, iterator end, StrictWeakOrdering cmp);
The is_heap() function returns true if the given range [start,end) is a heap.
If the strict weak ordering comparison function object cmp is given, then it is used instead of the < operator to compare elements.
is_heap() runs in linear time.