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Efficient Storage of and Access to Adjacency Lists

Efficient Storage of and Access to Adjacency Lists

Large graphs are stored as adjacency lists to save space. Traditional mechanisms based on arrays of pointers waste space. The following scheme is based on array of indices, which saves space and provides easier access.

Consider a weighted graph, G = (V, E), with |V|= n and |E| = m, where each edge and vertx has a weight.
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Below, the two given arrays store all the info necessary to represent the edges of the graph and to facilitate all operations on them efficiently:

 unsigned short xadj[n+1];unsigned short adjncy[m];adjncy[xadj[i]] to adjncy[xadj[i+1]] denote the edges from _vertex i, wherenumber of edges from vetex i = xadj[i+1] - xadj[i]

The weights of vertices and edges can be stored as arrays as follows:

 short edge_wgt[m];short vertex_wgt[n];
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