Standard C++ Library Copyright 1998, Rogue Wave Software, Inc.

pop_heap- Moves the largest element off the heap.

template <class RandomAccessIterator> void pop_heap(RandomAccessIterator first, RandomAccessIterator last); template <class RandomAccessIterator, class Compare> void pop_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 pro- perties are: 1. *ais the largest element in the range. 2. *amay be removed by the pop_heap algorithm or a new element may be added by the push_heap algorithm, inO(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 (in other words, thatfirstis the largest element in the heap or the first element based on the alternate comparison operator). It then swaps the value in the locationfirstwith the value in the locationlast-1and makes the range [first,last-1)back into a heap. You can then access the element inlastusing the vector or dequeback() member function, or you can remove the element using thepop_backmember function. Note that pop_heap does not actually remove the element from the data structure; you must use another function to do that.

pop_heap performs at most2*log(last-first) comparisons.

// // heap_ops.cpp // #include <algorithm> #include <vector> #include <iostream> using namespace std; 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; } Program 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 parame- ters, you always need to supply theAllocatortemplate argu- ment. For instance, you need to write:vector<int,allocator<int> > instead of:vector<int> If your compiler does not support namespaces, then you do not need the using declaration forstd.

make_heap, push_heap, sort_heap