Merge pull request #50 from taran-1407/patch-1

Adding GraphBuilder Utility

GraphBuilder/GraphBuilder.java

@@ -0,0 +1,31 @@
+class GraphBuilder{
+	public static int[][] makeGraph(int NumberOfNodes, int NumberOfEdges, int[] from, int[] to, boolean undirected){
+		int[][] graph = new int[NumberOfNodes][];
+		int[] outdegree = new int[NumberOfNodes];
+		for(int i = 0; i< NumberOfEdges; i++){
+		    outdegree[from[i]]++;
+		    if(undirected)outdegree[to[i]]++;
+		}
+		for(int i = 0; i< NumberOfNodes; i++)graph[i] = new int[outdegree[i]];
+		for(int i = 0; i< NumberOfEdges; i++){
+		    graph[from[i]][--outdegree[from[i]]] = to[i];
+		    if(undirected)graph[to[i]][--outdegree[to[i]]] = from[i];
+		}
+		return graph;
+	}
+
+	public static int[][][] makeGraphWithEdgeInfo(int NumberOfNodes, int NumberOfEdges, int[] from, int[] to, boolean undirected){
+		int[][][] graph = new int[NumberOfNodes][][];
+		int[] outdegree = new int[NumberOfNodes];
+		for(int i = 0; i< NumberOfEdges; i++){
+		    outdegree[from[i]]++;
+		    if(undirected)outdegree[to[i]]++;
+		}
+		for(int i = 0; i< NumberOfNodes; i++)graph[i] = new int[outdegree[i]][];
+		for(int i = 0; i< NumberOfEdges; i++){
+		    graph[from[i]][--outdegree[from[i]]] = new int[]{to[i], i, 0};
+		    if(undirected)graph[to[i]][--outdegree[to[i]]] = new int[]{from[i], i, 1};
+		}
+		return graph;
+	}
+}

GraphBuilder/GraphBuilderUsage.java

@@ -0,0 +1,34 @@
+class GraphBuilderUsage{
+	//Usage Exmaple
+	public static void makeGraphUsage(){
+		int N = 6, E = 8;
+		int[] from = new int[]{0,0,0,1,1,2,2,4};
+		int[] to = new int[]{2,4,5,4,5,3,4,5};
+
+		int[][] graph = GraphBuilder.makeGraph(N, E, from, to, true);
+		for(int i = 0; i< N; i++){
+			System.out.print(i+": ");
+			for(int j:graph[i])System.out.print(j+" ");
+			System.out.println();
+		}
+	}
+
+	//Usage Example
+	public static void makeGraphWithEdgeInfoUsage(){
+		int N = 6, E = 8;
+		int[] from = new int[]{0,0,0,1,1,2,2,4};
+		int[] to = new int[]{2,4,5,4,5,3,4,5};
+
+		int[][][] graph = GraphBuilder.makeGraphWithEdgeInfo(N, E, from, to, true);
+		for(int i = 0; i< N; i++){
+			System.out.print(i+": ");
+			for(int[] j:graph[i])System.out.print("["+j[0]+", "+j[1]+", "+j[2]+"],");
+			System.out.println();
+		}
+	}
+
+	public static void main(String[] args){
+		makeGraphUsage();
+		makeGraphWithEdgeInfoUsage();
+	}
+}

GraphBuilder/README.md

@@ -0,0 +1,40 @@
+# Class GraphBuilder
+
+Creates graph in form of jagged arrays (as compared to Arraylist) for directed as well as undirected graphs from given set of edges in 0 indexing.
+
+All members of this class are static, so no constructor defined.
+
+## Methods
+
+### makeGraph
+```
+public static int[][] makeGraph(int NumberOfNodes, int NumberOfEdges, int[] from, int[] to, boolean undirected)
+```
+Returns the adjacency list representation of graph with specified Number of Nodes and Edges and the edges specified in from and to arrays in 0-based indexing. If undirected is set to true, the edges are deemed to be undirected, otherwise directed.
+
+```graph[u]``` is the array of vertices having an edge outgoing from vertex u.
+
+** Constraints **
+* 0 \leq from[i], to[i] < NumberOfNodes
+* from.length = to.length = NumberOfEdges
+
+** Computational complexity **
+* $ O (NumberOfNodes + NumberOfEdges) $
+
+### makeGraphWithEdgeInfo
+```
+public static int[][][] makeGraphWithEdgeInfo(int NumberOfNodes, int NumberOfEdges, int[] from, int[] to, boolean undirected)
+```
+
+Returns the adjacency list representation of graph with specified Number of Nodes and Edges and the edges specified in from and to arrays in 0-based indexing. If undirected is set to true, the edges are deemed to be undirected, otherwise directed. This method also returns useful information about edge index and edge direction.
+
+```graph[u]``` is the array of tuples ```[v, idx, direction]``` where edge indexed ```idx``` is between node ```u``` and node ```v``` and direction takes value either $0$ or $1$.
+- If direction is $0$, edge indexed ```idx``` is from ```u``` to ```v```
+- If direction is $1$, edge indexed ```idx``` is from ```v``` to ```u```
+
+** Constraints **
+* 0 \leq from[i], to[i] < NumberOfNodes
+* from.length = to.length = NumberOfEdges
+
+** Computational complexity **
+* $ O (NumberOfNodes + NumberOfEdges) $