# C o n f i d e n t i a l HOME NEXT Subject Name: Data Structure Using C Unit Title: Graphs.

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C o n f i d e n t i a l HOME NEXT Subject Name: Data Structure Using C Unit Title: Graphs

C o n f i d e n t i a l Developed By Nitendra Graphs Recap Definition of Graph Type of Graphs Graph Representation An adjacency List Representation An adjacency Matrix Representation Graph Traversal Breath First Search (BFS) - Algorithm Depth First Search (DFS) - Algorithm Spanning Tree Kruskal’s Algorithm Prim’s Algorithm Class summary NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Recap Definition of Tree Terminologies Type of Trees – Complete Binary Tree – Full/Strictly Binary Tree – Binary Search Tree –Threaded Binary Tree – Red Black Tree – B Tree [Balance Tree] – AVL Tree Binary Tree Traversals Application of Trees HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Definition of Graph : A graph is a set of objects called points, nodes, or vertices connected by links called lines or edges. Mathematically we can represent graph as A graph G is defined as follows: G=(V,E), where V is a finite, non-empty set of vertices (singular: vertex) and E is a set of edges (links between pairs of vertices). Graphs Graph G HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Type of Graphs Graphs Graph G2 Undirected Graph: When the edges in a graph have no direction, the graph is called undirected. Directed Graph (Digraph) : When the edges in a graph have direction, the graph is called undirected. Graph G1 HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Graph G4 Strongly Connected Graph: Two vertices are said to be connected if there is a path between them. Furthermore, a directed graph is strongly connected if there is a path from each vertex to every other vertex in the digraph. Weakly Connected Graph: A directed graph is weakly connected if at least two vertices are not connected. Graph G3 HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Degree of a vertex : The degree of a vertex is the number of lines incident to it. - The outdegree of a vertex in a digraph is the number of arcs leaving the vertex. - The indegree is the number of arcs entering the vertex. Graph G3 The indegree of the vertex 4 is 2 and outdegree is 1 HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Graph Representation : Two main data structures for the representation of graphs are used in practice. To store the graph in memory we require these type of representation technique. An adjacency List Representation An adjacency Matrix Representation HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs An adjacency List Representation An adjacency list is the representation of all edges or arcs in a graph as a list. If the graph is undirected, every entry is a set of two nodes containing the two ends of the corresponding edge; if it is directed, every entry is a tuple of two nodes, one denoting the source node and the other denoting the destination node of the corresponding arc. A B C D E F HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs An adjacency Matrix Representation The adjacency matrix uses a vector (one-dimensional array) for the vertices and a matrix (two-dimensional array) to store the edges. (b) Adjacency matrix for directed graph HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Graph Traversal: Graph traversal refers to the problem of visiting all the nodes in a graph in a particular manner. Tree traversal is a special case of graph traversal. In contrast to tree traversal, in general graph traversal, each node may have to be visited more than once, and a root-like node that connects to all other nodes might not exist. There are TWO types of traversal algorithms Breath First Search (BFS) Depth First Search (DFS) During the execution of our algorithm each node N of Graph G will be in one of three states, called the status of N, as follows:- STATUS = 1 [ Ready State ] The initial state of the node N. STATUS = 2 [ Waiting Sate] The node N is on the queue or stack. Waiting to be processed STATUS = 3 [ Processed State] The node N has been processed. HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Breath First Search (BFS) - Algorithm Step – I : Initially all nodes to be ready state (STATUS =1) Step – II: Put the starting node A in the QUEUE and change its status to the waiting state (STATUS=2) Step –III: Repeat Step IV and V until QUEUE is empty Step –IV: Remove the front node N of QUEUE. Process N and change the status of N to the processed state (STATUS = 3) Step –V: Add to the rear of QUEUE all the neighbour of N that are in the ready state (STATUS =1) and change their status to the waiting state (STATUS=2) [End of Step –III Loop] Step –VI: Exit HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Breath First Search (BFS) - Example HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Breath First Search (BFS) - Example (Contd.) HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Breath First Search (BFS) - Example BFS Sequence is: A B C D E F HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Depth First Search (DFS) - Algorithm Step – I : Initially all nodes to be ready state (STATUS =1) Step – II: Put the starting node A in the STACK and change its status to the waiting state (STATUS=2) Step –III: Repeat Step IV and V until STACK is empty Step –IV: Pop the top node N of STACK. Process N and change its status to the processed state (STATUS = 3) Step –V: Push into STACK all the neighbour of N that are still in ready state (STATUS =1) and change their status to the waiting state (STATUS=2) [End of Step –III Loop] Step –VI: Exit HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Depth First Search (DFS) - Example HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Depth First Search (DFS) - Example (Contd.) DFS Sequence is: A B C D E HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Depth First Search (DFS) Vs Breath First Search (BFS) HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Spanning Tree: A spanning tree of a graph is an undirected tree consisting of only those edges necessary to connect all the nodes in the original graph. For any pair of nodes there exists only one path between them and the insertion of any edge to a spanning tree forms a unique cycle. A minimum spanning tree or minimum weight spanning tree is then a spanning tree with weight less than or equal to the weight of every other spanning tree. There are two types of algorithms Kruskal‘s Algorithm Prim’s Algorithm HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Kruskal’s Algorithm: This algorithm finds a minimum spanning tree for a connected weighted graph. This means it finds a subset of the edges that forms a tree that includes every vertex, where the total weight of all the edges in the tree is minimized. Kruskal's algorithm is an example of a greedy algorithm. Example: From the graph, draw a table with ascending order of weight. After that include one by one and reject the cyclic path. EdgeWeight Remarks AD5 CE5 DF6 AB7 BE7 BC8 X EF8 X BD9 X EG9 FG11 X DE15 X Cost: 39 HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Prim’s Algorithm: This algorithm in graph theory that finds a minimum spanning tree for a connected weighted graph. This means it finds a subset of the edges that forms a tree that includes every vertex, where the total weight of all the edges in the tree is minimized. Example: This is our original weighted graph. The numbers near the arcs indicate their weight Vertex D has been arbitrarily chosen as a starting point. Vertices A, B, E and F are connected to D through a single edge. A is the vertex nearest to D and will be chosen as the second vertex along with the edge AD. HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Prim’s Algorithm (Example Contd.) The next vertex chosen is the vertex nearest to either D or A. B is 9 away from D and 7 away from A, E is 15, and F is 6. F is the smallest distance away, so we highlight the vertex F and the arc DF. The algorithm carries on as above. Vertex B, which is 7 away from A, is highlighted. In this case, we can choose between C, E, and G. C is 8 away from B, E is 7 away from B, and G is 11 away from F. E is nearest, so we highlight the vertex E and the arc EB. HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Graphs Prim’s Algorithm (Example) Here, the only vertices available are C and G. C is 5 away from E, and G is 9 away from E. C is chosen, so it is highlighted along with the arc EC. Vertex G is the only remaining vertex. It is 11 away from F, and 9 away from E. E is nearer, so we highlight it and the arc EG. Now all the vertices have been selected and the minimum spanning tree is shown in green. In this case, it has weight 39. HOME NEXT PREVIOUS

C o n f i d e n t i a l Developed By Nitendra Class summary Definition of Graph Type of Graphs Graph Representation An adjacency List Representation An adjacency Matrix Representation Graph Traversal Breath First Search (BFS) - Algorithm Depth First Search (DFS) - Algorithm Spanning Tree Kruskal’s Algorithm Prim’s Algorithm HOME PREVIOUS

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