在C++ STL中,存在priority_queue可直接用于实现Max Heap。为了完全理解代码,请确保您熟悉C++中的以下概念
- STL中的容器适配器
- 函子
请参见以下示例:
CPP
// C++ program to show that priority_queue is by
// default a Max Heap
#include
using namespace std;
// Driver code
int main ()
{
// Creates a max heap
priority_queue pq;
pq.push(5);
pq.push(1);
pq.push(10);
pq.push(30);
pq.push(20);
// One by one extract items from max heap
while (pq.empty() == false)
{
cout << pq.top() << " ";
pq.pop();
}
return 0;
}
CPP
// C++ program to use priority_queue to implement min heap
#include
using namespace std;
// Driver code
int main ()
{
// Creates a min heap
priority_queue , greater > pq;
pq.push(5);
pq.push(1);
pq.push(10);
pq.push(30);
pq.push(20);
// One by one extract items from min heap
while (pq.empty() == false)
{
cout << pq.top() << " ";
pq.pop();
}
return 0;
}
C++
// C++ Progrma to implement min heap
// using default priority_queue(max-heap)
#include
#include
using namespace std;
int main()
{
// data
int arr[] = { 25, 7, 9, 15, 20, 36, 50 };
// default priority_queue using max-heap
priority_queue pq;
// size of the array
int n = sizeof(arr) / sizeof(arr[0]);
// multiply -1 with all elements while
// inserting
for (int i = 0; i < n; i++) {
pq.push((-1) * arr[i]);
}
// multiply all elements with -1 while
// retrive the elements
while (!pq.empty()) {
cout << (pq.top()) * (-1) << " ";
pq.pop();
}
return 0;
}
CPP
// C++ program to use priority_queue to implement Min Heap
// for user defined class
#include
using namespace std;
// User defined class, Point
class Point
{
int x;
int y;
public:
Point(int _x, int _y)
{
x = _x;
y = _y;
}
int getX() const { return x; }
int getY() const { return y; }
};
// To compare two points
class myComparator
{
public:
int operator() (const Point& p1, const Point& p2)
{
return p1.getX() > p2.getX();
}
};
// Driver code
int main ()
{
// Creates a Min heap of points (order by x coordinate)
priority_queue , myComparator > pq;
// Insert points into the min heap
pq.push(Point(10, 2));
pq.push(Point(2, 1));
pq.push(Point(1, 5));
// One by one extract items from min heap
while (pq.empty() == false)
{
Point p = pq.top();
cout << "(" << p.getX() << ", " << p.getY() << ")";
cout << endl;
pq.pop();
}
return 0;
}
输出
30 20 10 5 1
由于元素是按降序打印的,因此默认情况下我们有一个最大堆。如何实现Min Heap?
priority_queue支持一个构造函数,该构造函数需要两个额外的参数才能使其成为最小堆。
priority_queue , ComparisonType > min_heap;
第三个参数“比较类型”可以是必须具有bool作为返回类型且必须具有2个参数的函数或因子(aka函数对象)。
以下是整数的示例。
CPP
// C++ program to use priority_queue to implement min heap
#include
using namespace std;
// Driver code
int main ()
{
// Creates a min heap
priority_queue , greater > pq;
pq.push(5);
pq.push(1);
pq.push(10);
pq.push(30);
pq.push(20);
// One by one extract items from min heap
while (pq.empty() == false)
{
cout << pq.top() << " ";
pq.pop();
}
return 0;
}
输出 :
1 5 10 20 30
使用默认的priority_queue进行min-heap的另一种方法:
这在竞争性编程中经常使用。我们首先将所有元素乘以(-1)。然后,我们创建一个最大堆(最大堆是优先级队列的默认值)。当我们访问数据并想打印时,我们只需将这些元素再乘以(-1)。
下面是上述想法的实现:
C++
// C++ Progrma to implement min heap
// using default priority_queue(max-heap)
#include
#include
using namespace std;
int main()
{
// data
int arr[] = { 25, 7, 9, 15, 20, 36, 50 };
// default priority_queue using max-heap
priority_queue pq;
// size of the array
int n = sizeof(arr) / sizeof(arr[0]);
// multiply -1 with all elements while
// inserting
for (int i = 0; i < n; i++) {
pq.push((-1) * arr[i]);
}
// multiply all elements with -1 while
// retrive the elements
while (!pq.empty()) {
cout << (pq.top()) * (-1) << " ";
pq.pop();
}
return 0;
}
输出
7 9 15 20 25 36 50
如何制作用户定义类的最小堆?
让我们考虑下面的示例,在该示例中,我们构建了按X轴排序的2个D点的最小堆。
CPP
// C++ program to use priority_queue to implement Min Heap
// for user defined class
#include
using namespace std;
// User defined class, Point
class Point
{
int x;
int y;
public:
Point(int _x, int _y)
{
x = _x;
y = _y;
}
int getX() const { return x; }
int getY() const { return y; }
};
// To compare two points
class myComparator
{
public:
int operator() (const Point& p1, const Point& p2)
{
return p1.getX() > p2.getX();
}
};
// Driver code
int main ()
{
// Creates a Min heap of points (order by x coordinate)
priority_queue , myComparator > pq;
// Insert points into the min heap
pq.push(Point(10, 2));
pq.push(Point(2, 1));
pq.push(Point(1, 5));
// One by one extract items from min heap
while (pq.empty() == false)
{
Point p = pq.top();
cout << "(" << p.getX() << ", " << p.getY() << ")";
cout << endl;
pq.pop();
}
return 0;
}
输出 :
(1, 5)
(2, 1)
(10, 2)
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