c++ 判断给定区间是否是一个heap. O(N) (is_heap)

#include <iostream>     // cout
#include <algorithm>    // is_heap, make_heap, pop_heap
#include <vector>       // vector
using namespace std;
int main () {
    vector<int> foo {,,,,,,,,};

    if (!is_heap(foo.begin(),foo.end()))
        make_heap(foo.begin(),foo.end());

    cout << "Popping out elements:";
    while (!foo.empty()) {
        pop_heap(foo.begin(),foo.end());   // moves largest element to back
        cout << ' ' << foo.back();         // prints back
        foo.pop_back();                         // pops element out of container
    }
    cout << '\n';

    return ;
}