c++ make_heap, pop_heap, push_heap, sort_heap详解

来源：互联网发布：linux man help 编辑：程序博客网时间：2024/05/22 05:01

std::pop_heap是一个实现快排的库

将front（即第一个最大元素）移动到end的前部，同时将剩下的元素重新构造成(堆排序)一个新的heap。

时间复杂度是： (2*log(last - first))

例如：

#include <iostream>#include <vector>#include <algorithm> using namespace std; int main(){  int a[] = {100, 19, 36, 17, 3, 25, 1, 2, 7};  vector<int> v(a, a+9);   cout <<"\nHere are the values in the vector (the heap):\n";  for (vector<int>::size_type i=0; i<v.size(); i++)    cout <<v.at(i)<<" ";   cout <<"\nNow we delete (pop) a value from the heap.";  pop_heap(v.begin(), v.end());  cout <<"\nHere are the revised contents of the vector:\n";  for (vector<int>::size_type i=0; i<v.size(); i++)   cout <<v.at(i)<<" ";  cout <<"\nNote that the value deleted from the heap is still "         "\nin the vector (at the end of the vector).";   cout <<"\nSo, we should reduce the size of the vector by 1, which "         "we now do, and\nthen display the vector, which is once again a heap, one more time.";   v.resize(v.size()-1);  cout <<"\nHere are the final contents of the vector:\n";  for (vector<int>::size_type i=0; i<v.size(); i++)    cout <<v.at(i)<<" ";   return 0;}

其结果是：

Output:Here are the values in the vector (the heap):100 19 36 17 3 25 1 2 7Now we delete (pop) a value from the heap.Here are the revised contents of the vector:36 19 25 17 3 7 1 2 100Note that the value deleted from the heap is stillin the vector (at the end of the vector).So, we should reduce the size of the vector by 1, which we now do, andthen display the vector, which is once again a heap, one more time.Here are the final contents of the vector:36 19 25 17 3 7 1 2

理论－－－堆简介

堆并不是STL的组件，但是经常充当着底层实现结构。比如优先级队列（Priority Queue）等等。

堆是一种完全二叉树，因此我们可以用数组来存储所有节点。在这里的实现中，采用了一个技巧：将数组中索引为0的元素保留，设置为极大值或者为极小值（依据大顶堆或者小顶堆而定）。那么当某个节点的索引是i时，其左子节点索引为2*i，右子节点索引为2*i+1.父节点是i/2（这里/表示高斯符号，取整）。这种以数组表示树的方式，我们成为隐式表述法（implicit reprentation）。我们这里用C++ STL中的容器vector实现替代数组的功能。