cppreference.com > C++ Algorithms > is_heap is_heap 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. Related topics: make_heap pop_heap push_heap sort_heap