std::is_heap( ) in C++ with Examples

Last Updated : 21 May, 2020

The std::is_heap() function in C++ Standard Template Library is used to check whether a given range of elements forms Max Heap or not. It returns True when given ranges of elements forms Max Heap, else it returns False.

Header File:

#include <algorithm>

Syntax:

is_heap(first, last)

Parameter: It takes two parameters, iterators pointing towards the first and last element of the range.

Return Value: The function returns the following value:

True: If the elements in the range [first, last) forms a Max Heap.
False: If the elements in the range [first, last) doesn’t forms a Max Heap.

Below is the program to illustrate std::is_heap():

Program 1:

// C++ program to illustrate
// the std::is_heap()
  
#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
  
// Driver Code
int main()
{
  
    // Given list of numbers
    vector<int> arr = { 3, 1, 5, 1, 9, 8 };
  
    // Check if arr[] forms max-heap or not
    bool isHeap = is_heap(arr.begin(),
                          arr.end());
  
    if (isHeap) {
        cout << "Forms a Max Heap";
    }
    else {
        cout << "Doesn't forms a Max Heap";
    }
}

Output:

Doesn't forms a Max Heap

Program 2:

// C++ program to illustrate the std::is_heap()
  
#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
  
// Driver Code
int main()
{
  
    // Given list of numbers
    vector<int> arr = { 3, 1, 5, 1, 9, 8 };
  
    // Check if arr[] forms max-heap or not
    bool isHeap = is_heap(arr.begin(),
                          arr.end());
  
    // isHeap is false then make Max Heap
    // using in built function make_heap
    if (!isHeap) {
        make_heap(arr.begin(), arr.end());
    }
  
    // Else already a heap
    else {
        cout << "Already Max Heap\n";
    }
  
    // Print all the elements of arr
    // after make Max Heap
    for (auto& it : arr) {
        cout << it << ' ';
    }
    return 0;
}

Output:

9 3 8 1 1 5

Reference: http://www.cplusplus.com/reference/algorithm/is_heap/

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