Hey, I have to code a min-heap, along with other things to help compute minimum spanning tree.
I coded up the min-heap pretty easily and I have no compile errors, however my delete fix up does not seem to be working properly.
For example, I insert these ints into an empty min heap:
10, 9, 7, 2, 5, 3, 8, 4.
I get the min-heap:
2, 4, 3, 5, 7, 9, 8, 10
After the first extract minimum call I get the min-heap:
3, 4, 8, 5, 7, 9, 10
Which is correct, however, if I call min-heap again I get this heap:
8, 4, 10, 5, 7, 9
Which is incorrect, I've check my code and I still can't find the problem.
My min-heap consist of "edges" and not ints. An edge is a class that consist of 3 ints that represent two vertices and a cost. My min-heap is sorted by cost.
Here is the header file:
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/*
* File: heap.h
* Author: Owner
*
* Created on April 24, 2010, 10:51 PM
*/
#ifndef _HEAP_H
#define _HEAP_H
#include <vector>
#include "edge.h"
using namespace std;
class min_heap
{
public:
min_heap(int size);
~min_heap();
int get_min();
void extract_min();
bool isEmpty();
void insert(edge newEdge);
void bottom_up(int i);
void top_down(int i);
void display();
void heapify(int i);
vector<edge> theEdges;
// private:
int heapSize;
int arraySize;
int* data;
int parent(int i);
int lchild(int i);
int rchild(int i);
};
#endif /* _HEAP_H */
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Here is my heap.cpp file:
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#include <vector>
#include "heap.h"
#include "edge.h"
#include <string>
#include <iostream>
using namespace std;
min_heap::min_heap(int size)
{
arraySize = 0;
heapSize = 0;
theEdges.resize(size);
}
min_heap::~min_heap()
{
delete[] data;
}
int min_heap::parent(int i)
{
//return i/2;
return (i-1)/2;
}
int min_heap::lchild(int i)
{
//return 2*i;
return 2*(i+1);
}
int min_heap::rchild(int i)
{
//return 2*i+1;
return 2*i+2;
}
bool min_heap::isEmpty()
{
return (heapSize == 0);
}
int min_heap::get_min()
{
if(isEmpty())
;
// throw string("empty the heap is");
else
return theEdges[0].cost;
}
void min_heap::bottom_up(int i)
{
int p;
int temp;
if(i != 0)
{
p = parent(i);
if(theEdges[p].cost > theEdges[i].cost)
{
temp = theEdges[p].cost;
theEdges[p].cost = theEdges[i].cost;
theEdges[i].cost = temp;
bottom_up(p);
}
}
}
void min_heap::top_down(int i)
{
int min_element;
int temp;
int left = lchild(i);
int right = rchild(i);
if(right >= heapSize)
{
if(left >= heapSize)
return;
else
min_element = left;
}
else
{
if(theEdges[left].cost <= theEdges[right].cost)
min_element = left;
else
min_element = right;
}
if(theEdges[i].cost> theEdges[min_element].cost)
{
temp = data[min_element];
theEdges[min_element].cost = theEdges[i].cost;
theEdges[i].cost = temp;
top_down(min_element);
}
}
void min_heap:: insert(edge newEdge)
{
theEdges[heapSize] = newEdge;
//top_down(heapSize-1);
bottom_up(heapSize);
heapSize++;
}
void min_heap::extract_min()
{
theEdges[0] = theEdges[heapSize-1];
heapSize--;
if(heapSize> 0)
{
heapify(0);
//top_down(0);
}
}
void min_heap::display()
{
for(int i = 0; i < heapSize; i++)
cout<< "i is: " << i << ", data is: " << theEdges[i].cost << ", " << endl;;
}
void min_heap:: heapify(int i)
{
int left = lchild(i);
int right = rchild(i);
int smallest;
int temp;
if(left <= heapSize && theEdges[left].cost < theEdges[i].cost)
smallest = left;
else
smallest = i;
if(right <= heapSize && theEdges[right].cost < theEdges[smallest].cost)
smallest = right;
if(smallest != i)
{
temp = theEdges[smallest].cost;
theEdges[smallest].cost = theEdges[i].cost;
theEdges[i].cost = temp;
heapify(smallest);
}
}
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The deletion fix up was the "top_down" function, but that didn't seem to work. So I created the "heapify" function, and that gives me the problem that I stated above. Any help at all would be appreciated.
Here is the edge.h file if needed:
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/*
* File: edge.h
* Author: Owner
*
* Created on April 28, 2010, 3:30 PM
*/
#ifndef _EDGE_H
#define _EDGE_H
class edge
{
public:
int u;
int v;
int cost;
edge()
{
u = -1;
v = -1;
cost = -1;
}
edge (int vertex1,int vertext2,int theCost)
{
u = vertex1;
v = vertext2;
cost = theCost;
}
};
#endif /* _EDGE_H */
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