# CSC 316 Programming Project #3 – Kruskal’s Algorithm for Minimum Spanning Trees solution

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## Description

Project Objectives
This task deals with Minimum Spanning Trees (MST) on weighted graphs. More specifically, you
will implement Kruskal’s MST algorithm. MST problems arise very often, especially in applications
related to computer networks. Furthermore, an efficient implementation of Kruskal’s algorithm
requires a number of the data structures we have discussed in class (i.e., heaps, up-trees and the
union-find algorithms, and graphs), and you will have the opportunity to integrate all of them in
a single program.
Input
Each line of the input file will represent one edge in an undirected graph. It will contain two
integers – the endpoints of the edge – followed by a real number – the weight of the edge. You may
assume that the vertices are numbered 0 through n, that n < 1000, and that the number of edges,
m, is such that m < 5000. The last line of the file will contain -1, to denote the end of input. You
are not expected to check the input for errors of any sort.
Files graph1 and graph2 in the Project3 directory are sample input files. The output of your
program will be tested on an input file not available in advance.
Description
• construct an edge record for it (consisting of four fields, vertex1, vertex2, weight, and
next),
• insert the record for e in the adjacency list of the two vertices,
• insert the edge into a heap.
Since the number of edges will be less than 5000, you can represent the heap as an array of 5000 edge
records; the key (priority) of each edge will be its weight. Obviously, you will need to implement the
heap operations insert and deleteMin [Note: Kruskal’s algorithm may be implemented without
using a heap. One can sort the edges and consider them in increasing weight. This is strongly
discouraged in this task, and the output has been designed so that you will need to implement a
heap.]
In order to implement Kruskal’s algorithm, you also need to implement the up-tree operations
to keep track of how connected components change during the execution of the algorithm. Since
vertices will be numbered 0 through n (your program should determine n), you can use the array
implementation described in class1
. Initially, each vertex is in a connected component by itself, and
adding an edge between two components has the effect of a union operation. Make sure that you
implement a balanced version of union, but regarding the find operation, you may implement it
with or without path compression.
1
It should not be hard to modify the find and union algorithms to work for the array representation of up-trees.
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Finally, you are free to choose any of the data structures we have discussed in class (e.g., linked
lists, search trees, etc.) to implement the set of edges in the MST that Kruskal’s algorithm returns.
Deliverables: Source Code and Output
The programs you submit will prompt the user for the names of the input and output files. Specifically, your code will implement:
1. The heap structure, and the insert and deleteMin operations, using an array-based implementation.
2. The up-tree structure, along with the union and find operations; use an array representation
of up-trees.
3. An adjacency list representation of graphs.
4. Kruskal’s algorithm for computing the MST of a graph.
Since we need to test whether you have implemented all data structures and operations described
above, your program will print the content of several data structures, as follows.
Printing the Heap. Once all the edges have been read in and the heap (partially ordered by
edge weight) constructed, your program will print the contents of the heap array in m lines (recall
that m is also the number of edges in the graph). Each line i will represent the edge in position
i of the heap. Each line should have exactly 9 characters: the first endpoint of the edge, right
justified in a field of 4; a space; then the second endpoint, also right justified in a field of 4. The
first number must always be less than the second. If an edge joins vertices 634 and 43, the output
should contain the line
⊔⊔43⊔⊔634
Printing the MST. Once your program has computed the MST, it will print n lines, each representing one edge of the MST. Each line should have 9 characters, exactly as described above.
Furthermore, the edges must appear in the output in lexicographic order: all the edges on vertex
0 first, then those on 1, etc. Also, all the edges of vertex 0 must be sorted according to the second
vertex, etc2
. The output from the sample input files graph1 and graph2 are in files graph1 output
and graph2 output.
Printing the Adjacency List. Finally, your program will print n + 1 lines, each corresponding
to one of the n + 1 vertices of the graph. The i-th line, i = 0, · · · , n, will contain, in increasing
order, all the vertices that are adjacent to vertex i (but not vertex i itself). Each vertex should be
right justified in a field of 4 characters, with vertices printed on the same line separated by a space.
Obey the format carefully. The output of your program will be verified automatically with the diff
utility.
Example
Suppose that the input to your program corresponds to the graph shown in Figure 1:
2There are different ways to accomplish this, depending on how you have decided to implement the set of edges
of the MST. If you have chosen to represent the set of edges as a linked list, for instance, you may want to keep the
list sorted by the first vertex, and also sort edges with the same first vertex according to the second vertex.
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0
3 2
1
5.0
6.0
10.0
14.0
12.0
7.0
Figure 1: Graph for example input
2 0 7.0
3 2 12.0
0 3 14.0
1 0 5.0
3 1 10.0
1 2 6.0
-1
Edges are inserted into the heap in the order given. Let e0 be the first edge (of weight 7.0), e1 the
second edge (of weight 12.0), and so on. The array representing the final heap, after all insertions
have taken place, will contain the edges in this order: e3, e0, e5, e1, e4, e2. The MST contains edges
e3, e5, and e4. The output of your program should be 13 lines: the first 6 are the contents of the
heap of edges after all insertions3
, the next 3 lines are the edges of the MST, sorted by vertex, and
the last four lines are the adjacency list.
⊔⊔⊔0⊔⊔⊔⊔1
⊔⊔⊔0⊔⊔⊔⊔2
⊔⊔⊔1⊔⊔⊔⊔2
⊔⊔⊔2⊔⊔⊔⊔3
⊔⊔⊔1⊔⊔⊔⊔3
⊔⊔⊔0⊔⊔⊔⊔3
⊔⊔⊔0⊔⊔⊔⊔1
⊔⊔⊔1⊔⊔⊔⊔2
⊔⊔⊔1⊔⊔⊔⊔3
⊔⊔⊔1⊔⊔⊔⊔2⊔⊔⊔⊔3
⊔⊔⊔0⊔⊔⊔⊔2⊔⊔⊔⊔3
⊔⊔⊔0⊔⊔⊔⊔1⊔⊔⊔⊔3
⊔⊔⊔0⊔⊔⊔⊔1⊔⊔⊔⊔2
Submission: Submit all your programs by the due date indicated on the course site.
3Note that edge e3 is given in the input file as {1, 0}, but in the output it appears as {0, 1}.
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