107 lines
1.6 KiB
C
107 lines
1.6 KiB
C
/**
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* Warshall's algorithm for transitive closure computation.
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*/
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#include "warshall.h"
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#include "debug.h"
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void
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graph_fill (int *graph, int nodes, int value)
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{
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int node;
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node = 0;
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while (node < (nodes * nodes))
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{
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graph[node] = value;
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node++;
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}
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}
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//! Show a graph
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void
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graph_display (int *graph, int nodes)
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{
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int i;
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int index (const int i, const int j)
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{
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return (i * nodes + j);
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}
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i = 0;
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while (i < nodes)
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{
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int j;
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j = 0;
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while (j < nodes)
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{
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eprintf ("%i ", graph[index (i, j)]);
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j++;
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}
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eprintf ("\n");
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i++;
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}
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}
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//! Apply warshall's algorithm to determine the closure of a graph
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/**
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* If j<i and k<j, then k<i.
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* Could be done more efficiently but that is irrelevant here.
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*
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*@param graph A pointer to the integer array of nodes*nodes elements.
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*@param nodes The number of nodes in the graph.
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*@Returns 0 if there is a cycle; and the algorithm aborts, 1 if there is no cycle and the result is okay.
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*/
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int
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warshall (int *graph, int nodes)
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{
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int i;
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int index (const int i, const int j)
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{
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return (i * nodes + j);
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}
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i = 0;
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while (i < nodes)
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{
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int j;
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j = 0;
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while (j < nodes)
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{
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if (graph[index (j, i)] == 1)
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{
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int k;
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k = 0;
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while (k < nodes)
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{
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if (graph[index (k, j)] == 1)
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{
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if (k == i)
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{
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// Oh no! A cycle.
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graph[index (k, i)] = 2;
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#ifdef DEBUG
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if (DEBUGL (5))
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{
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graph_display (graph, nodes);
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}
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#endif
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return 0;
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}
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graph[index (k, i)] = 1;
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}
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k++;
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}
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}
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j++;
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}
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i++;
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}
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return 1;
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}
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