C++ Algorithm Library - is_heap() Function


The C++ function std::algorithm::is_heap() tests whether given sequence is max heap or not. It uses operator< for comparison.


Following is the declaration for std::algorithm::is_heap() function form std::algorithm header.


template <class RandomAccessIterator>
bool is_heap(RandomAccessIterator first, RandomAccessIterator last);


  • first − Random access iterator to the initial position.

  • last − Random access iterator to the final position.

Return value

Returns true if given sequence is max heap otherwise returns false.


Throws exception if either the element comparison or an operation on an iterator throws exception.

Please note that invalid parameters cause undefined behavior.

Time complexity



The following example shows the usage of std::algorithm::is_heap() function.

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main(void) {
   vector<int> v = {3, 5, 2, 1, 4};
   bool result;

   result = is_heap(v.begin(), v.end());

   if (result == false)
      cout << "Given sequence is not a max heap." << endl;

   v = {5, 4, 3, 2, 1};

   result = is_heap(v.begin(), v.end());

   if (result == true)
      cout << "Given sequence is a max heap." << endl;

Let us compile and run the above program, this will produce the following result −

Given sequence is not a max heap.
Given sequence is a max heap.