Algorithm
Creates a heap.
#include <algorithm>
template <class RandomAccessIterator>
void
make_heap(RandomAccessIterator first,
RandomAccessIterator last);
template <class RandomAccessIterator, class Compare>
void
make_heap(RandomAccessIterator first,
RandomAccessIterator last, Compare comp);
A heap is a particular organization of elements in a range between two random access iterators [a, b). Its two key properties are:
*a is the largest element in the range.
*a may be removed by the pop_heap algorithm, or a new element can be added by the push_heap algorithm, in O(logN) time.
These properties make heaps useful as priority queues.
The heap algorithms use less than (operator<) as the default comparison. In all of the algorithms, an alternate comparison operator can be specified.
The first version of the make_heap algorithm arranges the elements in the range [first, last) into a heap using less than (operator<) to perform comparisons. The second version uses the comparison operator comp to perform the comparisons. Since the only requirements for a heap are the two listed above, make_heap is not required to do anything within the range (first, last - 1).
This algorithm makes at most 3 * (last - first) comparisons.
//
// heap_ops.cpp
//
#include <algorithm>
#include <vector>
#include <iostream.h>
int main(void)
{
int d1[4] = {1,2,3,4};
int d2[4] = {1,3,2,4};
// Set up two vectors
vector<int> v1(d1,d1 + 4), v2(d2,d2 + 4);
// Make heaps
make_heap(v1.begin(),v1.end());
make_heap(v2.begin(),v2.end(),less<int>());
// v1 = (4,x,y,z) and v2 = (4,x,y,z)
// Note that x, y and z represent the remaining
// values in the container (other than 4).
// The definition of the heap and heap operations
// does not require any particular ordering
// of these values.
// Copy both vectors to cout
ostream_iterator<int> out(cout," ");
copy(v1.begin(),v1.end(),out);
cout << endl;
copy(v2.begin(),v2.end(),out);
cout << endl;
// Now let's pop
pop_heap(v1.begin(),v1.end());
pop_heap(v2.begin(),v2.end(),less<int>());
// v1 = (3,x,y,4) and v2 = (3,x,y,4)
// Copy both vectors to cout
copy(v1.begin(),v1.end(),out);
cout << endl;
copy(v2.begin(),v2.end(),out);
cout << endl;
// And push
push_heap(v1.begin(),v1.end());
push_heap(v2.begin(),v2.end(),less<int>());
// v1 = (4,x,y,z) and v2 = (4,x,y,z)
// Copy both vectors to cout
copy(v1.begin(),v1.end(),out);
cout << endl;
copy(v2.begin(),v2.end(),out);
cout << endl;
// Now sort those heaps
sort_heap(v1.begin(),v1.end());
sort_heap(v2.begin(),v2.end(),less<int>());
// v1 = v2 = (1,2,3,4)
// Copy both vectors to cout
copy(v1.begin(),v1.end(),out);
cout << endl;
copy(v2.begin(),v2.end(),out);
cout << endl;
return 0;
}
Output :
4 2 3 1
4 3 2 1
3 2 1 4
3 1 2 4
4 3 1 2
4 3 2 1
1 2 3 4
1 2 3 4
If your compiler does not support default template parameters then you need to always supply the Allocator template argument. For instance you'll have to write:
vector<int,allocator>
instead of:
vector<int>
pop_heap, push_heap, and sort_heap