pop_heap (3C++std) - Tru64 UNIX
Standard C++ LibraryCopyright 1996, Rogue Wave Software, Inc. NAME
pop_heap - Moves the largest element off the heap.
SYNOPSIS
template <class RandomAccessIterator>
void
pop_heap(RandomAccessIterator first,
RandomAccessIterator last);
template <class RandomAccessIterator, class Compare>
void
pop_heap(RandomAccessIterator first,
RandomAccessIterator last, Compare comp);
DESCRIPTION
A heap is a particular organization of elements in a range between two
random access iterators [a, b). Its two key properties are:
1. *a is the largest element in the range.
2. *a may be removed by the pop_heap algorithm or a new element added by
the push_heap algorithm, in O(logN) time.
These properties make heaps useful as priority queues.
The pop_heap algorithm uses the less than (<) operator as the default
comparison. An alternate comparison operator can be specified.
The pop_heap algorithm can be used as part of an operation to remove the
largest element from a heap. It assumes that the range [first, last) is a
valid heap (i.e., that first is the largest element in the heap or the
first element based on the alternate comparison operator). It then swaps
the value in the location first with the value in the location last - 1 and
makes [first, last -1)back into a heap. You can then access the element
in last using the vector or deque back() member function, or remove the
element using the pop_back member function. Note that pop_heap does not
actually remove the element from the data structure, you must use another
function to do that.
COMPLEXITY
pop_heap performs at most 2 * log(last - first) comparisons.
EXAMPLE
//
// 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,char> 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
WARNING
If your compiler does not support default template parameters, you need to
always supply the Allocator template argument. For instance, you need to
write :
vector<int, allocator<int> >
instead of :
vector<int>
SEE ALSO
make_heap, push_heap, sort_heap
STANDARDS CONFORMANCE
ANSI X3J16/ISO WG21 Joint C++ Committee
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