trouble implementing Brovuka's Algorithm for finding a MST - c++

Question

i dunno why when running the code , there is access violation in the find function in the 1st loop , i am kinda lost , here is my code, if you guys any exisiting brovuka's c++ or java implementation that exists ?
#include <iostream>
using namespace std;
int numVertices,numEdges;
int *parent,*weight,numTrees;
int *bestEdgeNum;
struct edge {
int tail,head,weight;
};
typedef struct edge edgeType;
edgeType *edgeTab;
int find(int x)
{
int i,j,root;
for (i=x;parent[i]!=i; i=parent[i]);
root=i;
// path compression
for (i=x; parent[i]!=i;j=parent[i],parent[i]=root,i=j);
return root;
}
void makeEquivalent(int i,int j)
{
if (weight[i]>weight[j])
{
parent[j]=i;
weight[i]+=weight[j];
}
else
{
parent[i]=j;
weight[j]+=weight[i];
}
numTrees--;
}
int main()
{
int i,MSTweight=0;
int root1,root2;
int usefulEdges;
cout << "Enter the number of Vertices\n";
cin >> numVertices;
cout << "Enter the number of Edges\n";
cin >> numEdges;
edgeTab = new edgeType[numEdges];
parent = new int[numVertices];
weight = new int[numVertices];
bestEdgeNum = new int[numVertices];
if (!edgeTab || !parent || !weight || !bestEdgeNum)
{
cout << "error\n";
}
cout << "Enter the undirected edge weights for the graph in the format u v w\n";
for (i=0;i<numEdges;i++)
{
cin >> edgeTab[i].tail >> edgeTab[i].head >> edgeTab[i].weight;
}
for (i=0;i<numVertices;i++)
{
parent[i]=i;
weight[i]=1;
}
numTrees=numVertices; // Each vertex is initially in its own subtree
usefulEdges=numEdges; // An edge is useful if the two vertices are separate
while (numTrees>1 && usefulEdges>0)
{
for (i=0;i<numVertices;i++)
bestEdgeNum[i]=(-1);
usefulEdges=0;
for (i=0;i<numEdges;i++)
{
root1=find(edgeTab[i].tail);
root2=find(edgeTab[i].head);
if (root1==root2)
cout << edgeTab[i].tail <<" , " << edgeTab[i].head << " : "
<< edgeTab[i].weight << " is useless\n";
else
{
usefulEdges++;
if (bestEdgeNum[root1] == -1||edgeTab[bestEdgeNum[root1]].weight>edgeTab[i].weight)
bestEdgeNum[root1]=i; // Have a new best edge from this component
if (bestEdgeNum[root2]==(-1)|| edgeTab[bestEdgeNum[root2]].weight>edgeTab[i].weight)
bestEdgeNum[root2]=i; // Have a new best edge from this component
}
}
for (i=0;i<numVertices;i++)
if (bestEdgeNum[i]!=(-1))
{
root1=find(edgeTab[bestEdgeNum[i]].tail);
root2=find(edgeTab[bestEdgeNum[i]].head);
if (root1==root2)
continue; // This round has already connected these components.
MSTweight+=edgeTab[bestEdgeNum[i]].weight;
cout << edgeTab[bestEdgeNum[i]].tail << " " << edgeTab[bestEdgeNum[i]].head << " " << edgeTab[bestEdgeNum[i]].weight << "included in MST\n";
makeEquivalent(root1,root2);
}
cout << "numTrees is " << numTrees << endl;
}
if (numTrees!=1)
cout << "MST does not exist\n";
cout << "Sum of weights of spanning edges is " << MSTweight << endl;
return 0;
}

Answer 1

Your problem is that you are entering the vertices in 1 based format, but all your arrays (such as parent) are in 0 based format. When you try to get parent[4] bad things happen.
Probably the easiest fix is to subtract 1 from the head and tail when they are entered, then add 1 again when printing the results out.