Question

我有一个二进制堆实现，如下所示：
我必须弄清楚代码末尾显示错误输出的原因。

打印后我还需要删除myminheap对象，逐个弹出元素！

heap.h

#include <cstdlib>
#include <vector>
#include <iterator>

using namespace std;

class Heap
{
  public:
    Heap() {}
    ~Heap() {}

    vector <int> heap;
    int left(int parent);
    int right(int parent);
    int parent(int child);
    int size()                  {return heap.size();}
    void print();
};

class MinHeap : public Heap
{
  private:
    void heapify_up(int index);
    void heapify_down(int index);

  public:
    MinHeap() {}
    ~MinHeap() {}

    int pop_min();
    void insert(int element);
};

class MaxHeap : public Heap
{
  private:
    void heapify_up(int index);
    void heapify_down(int index);

  public:
    MaxHeap() {}
    ~MaxHeap() {}

    int pop_max();
    void insert(int element);
};

heap.cc

#include <cstdlib>
#include <iostream>
#include <vector>
#include <iterator>

using namespace std;

#include "heap.h"

//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
int Heap::left(int parent)
{
    int i = (parent << 1) + 1;  //2 * parent + 1    read more on bit shifts
    return (i < heap.size()) ? i : -1;
}

int Heap::right(int parent)
{
    int i = (parent << 1) + 2;
    return (i < heap.size()) ? i : -1;
}

int Heap::parent(int child)
{
    if(child){
        int i = (child >> 1) - 1;
        return i;
    }
    else return -1;
}

void Heap::print()
{
    vector<int>::iterator i = heap.begin();
    cout << "Heap = ";
    while(i != heap.end()){
        cout << *i << " ";
        i++;
    }
    cout << endl;
}
//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
int MinHeap::pop_min()
{
    int min = heap.front();
    heap[0] = heap[heap.size() - 1];
    heap.pop_back();
    heapify_down(0);
    return min;
}

void MinHeap::insert(int element)
{
    heap.push_back(element);
    heapify_up(heap.size() - 1);
}

void MinHeap::heapify_up(int index)
{
    while(index > 0 && parent(index) >= 0 && heap[parent(index)] > heap[index]){
        int temp = heap[index];
        heap[index] = heap[parent(index)];
        heap[parent(index)] = temp;
        index = parent(index);
    }
}

void MinHeap::heapify_down(int index)
{
    int child = left(index);

    if(child > 0 && right(index) > 0 && heap[child] > heap[right(index)])
        child = right(index);

    if(heap[index] > heap[child]){
        int temp = heap[child];
        heap[child] = heap[index];
        heap[index] = temp;
        heapify_down(child);
    }
}
//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
int MaxHeap::pop_max()
{
    int max = heap.front();
    heap[0] = heap[heap.size() - 1];
    heap.pop_back();
    heapify_down(0);
    return max;
}

void MaxHeap::insert(int element)
{
    heap.push_back(element);
    heapify_up(heap.size() - 1);
}

void MaxHeap::heapify_up(int index)
{
    while(index > 0 && parent(index) >= 0 && heap[parent(index)] < heap[index]){
        int temp = heap[index];
        heap[index] = heap[parent(index)];
        heap[parent(index)] = temp;
        index = parent(index);
    }
}

void MaxHeap::heapify_down(int index)
{
    int child = left(index);

    if(child > 0 && right(index) > 0 && child < right(index))
        child = right(index);

    if(heap[index] < heap[child]){
        int temp = heap[child];
        heap[child] = heap[index];
        heap[child] = temp;
        heapify_down(child);
    }
}
//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
//              test program
//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
int main(){
    // Create the heap
    MinHeap* myminheap = new MinHeap();
    myminheap->insert(700);
    myminheap->print();
    myminheap->insert(500);
    myminheap->print();
    myminheap->insert(100);
    myminheap->print();
    myminheap->insert(800);
    myminheap->print();
    myminheap->insert(200);
    myminheap->print();
    myminheap->insert(400);
    myminheap->print();
    myminheap->insert(900);
    myminheap->print();
    myminheap->insert(1000);
    myminheap->print();
    myminheap->insert(300);
    myminheap->print();
    myminheap->insert(600);
    myminheap->print();

    // Get priority element from the heap
    int heapSize = myminheap->size();
    for ( int i = 0; i < heapSize; i++ )
        cout << "Get min element = " << myminheap->pop_min() << endl;

    return 1;
}

这会产生乱码输出，如下所示：

Heap = 700 
Heap = 700 500 
Heap = 100 500 700 
Heap = 100 500 700 800 
Heap = 100 200 700 800 500 
Heap = 100 200 700 800 500 400 
Heap = 100 200 700 800 500 400 900 
Heap = 100 200 700 800 500 400 900 1000 
Heap = 100 200 700 300 500 400 900 1000 800 
Heap = 100 200 700 300 500 400 900 1000 800 600 
Get min element = 100
Get min element = 200
Get min element = 300
Get min element = 500
Get min element = 73
Get min element = 400
Get min element = 600
Get min element = 700
Get min element = 800
Get min element = 900

Answer 1

两个错误;下面的代码修复了它们（我已经将位移更改为mult / div - 这没有区别。当自然表达式为mult / div by 2时，为什么会想要使用移位。如果您正在考虑优化那么，好吧）。错误是什么，我把它留作练习......

// Num 1
int Heap::parent(int child)
{
    if(child > 0){
        int i = (child / 2);
        return i;
    }
    else return -1;
}

// Num 2
void MinHeap::heapify_down(int index)
{
    int child = left(index);

    if(child > 0 && right(index) > 0 && heap[child] > heap[right(index)])
        child = right(index);

    if(child > 0 && heap[index] > heap[child]){
        int temp = heap[child];
        heap[child] = heap[index];
        heap[index] = temp;
        heapify_down(child);
    }
}

你必须删除myminheap。逐个弹出元素并不意味着当容器中的元素数量达到0时自动销毁容器。

二进制最小堆：打印未存储的值

1 个答案: