Heaps using the vector class

takachi · #1 14-Dec-2008, 10:42

hello.I've written a function which is supposed to get an index of a vector and checks for the value of that index in the vector if it is smaller than his children and if so than replaces between the two and calls the function again in recursion with the bigger son's index.the problem is that I get a segmentation fault when I try to activate the function.
here is the program:

CPP / C++ / C Code:

#include <iostream>
#include <vector>
using std::cout;
using std::endl;


class Heap {
		public:
		vector<int> HeapVec;

		void rebuildHeap(int index)
		{
			if (index*2<(int)HeapVec.size()) //if there are 2 sons
			{
				int maxSonIndex;
				if (HeapVec[2*index]>=HeapVec[2*index+1])//if the left son is bigger than the right one
					maxSonIndex=2*index;
				else
					maxSonIndex=2*index+1;
				if (HeapVec[maxSonIndex]>HeapVec[index]) //if the son is bigger than his father
				{	//replacing between son and father
					int temp=HeapVec[index];
					HeapVec[index]=HeapVec[maxSonIndex];
					HeapVec[maxSonIndex]=temp;
					rebuildHeap(maxSonIndex); //call again to function with the new son
				}
			}
			else if (index*2==HeapVec.size()) //if there is only one son
			{
				if (HeapVec[2*index]>HeapVec[index]) //if the son is bigger than his father
                		{       //replacing between son and father     
                        		int temp=HeapVec[index]; 
                        		HeapVec[index]=HeapVec[2*index];
                        		HeapVec[2*index]=temp;          
                        		rebuildHeap(2*index); //call again to function with the new son
       	         		}  
			}
		}

};
int main()
{
	int i;
	Heap h;
	h.HeapVec[0]=17;
	h.HeapVec[1]=11;
	h.HeapVec[2]=17;
	h.HeapVec[3]=10;
	h.HeapVec[4]=9;
	h.HeapVec[5]=12;
	h.HeapVec[6]=15;
	h.HeapVec[7]=6;
	h.HeapVec[8]=2;
	h.HeapVec[9]=8;
	h.HeapVec[10]=9;
	
	h.rebuildHeap(0);
	for(i=0;i<=10;i++)
		cout<<h.HeapVec[i]<<endl;



}

can you tell me where is the bugg or how to fix it because I really have no clue.
thank you in advance.

takachi · #2 14-Dec-2008, 10:46

I've found the error.but I have a qeustion:why can't I initialize a vector like an array? I've used push_back() instead but it pushes it to the top of the vector.

davekw7x · #3 14-Dec-2008, 13:13

Quote:

Originally Posted by takachi

...why can't I initialize a vector like an array?...

The vector class has an "iterator consctuctor" that you can use to initialize a vector from an array:

CPP / C++ / C Code:

#include <iostream>
#include <vector>

using namespace std;

int main()
{
    int v_values[] = {11, 22, 33, 44, 55};
    int num_values = sizeof(v_values)/sizeof(v_values[0]);
    cout << "Number of elements in the v_values array = " << num_values << endl;

    //
    // The iterator constructor can convert array address values to interators
    //
    vector <int> ivector(v_values, v_values+num_values);
    cout << "ivector.size() = " << ivector.size() << endl;

    for (unsigned i = 0; i < ivector.size(); i++) {
        cout << "ivector[" << i << "] = " << ivector[i] << endl;
    }
    return 0;
}

Output

Code:

Number of elements in the v_values array = 5
ivector.size() = 5
ivector[0] = 11
ivector[1] = 22
ivector[2] = 33
ivector[3] = 44
ivector[4] = 55

Regards,

Dave

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Heaps using the vector class

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