63 lines
1.9 KiB
Text
63 lines
1.9 KiB
Text
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/* take infinity to be int max value, assume shortest path is shorter than this */
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global infinity = 9223372036854775807;
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/* takes number of vertices n (ints 0 to n -1), number of edges, edge list (u, v, w) of weighted directed graph, source vertex
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computes length of shortest path from source vertex to every vertex, distances invalid if negative cycles exist
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*/
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int[] bellman_ford(int n, int m, int[][] edges, int source) {
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var distance = new int[n];
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for (var i = 0; i < n; i = i + 1;) {
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distance[i] = infinity;
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}
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distance[source] = 0;
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for (var i = 0; i < n - 1; i = i + 1;) {
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for(var j = 0; j < m; j = j + 1;) {
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var edge = edges[j];
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var u = edge[0];
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var v = edge[1];
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var w = edge[2];
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if (distance[u] + w < distance[v]) {
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distance[v] = distance[u] + w;
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}
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}
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}
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/* check negative cycles */
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for(var j = 0; j < m; j = j + 1;) {
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var edge = edges[j];
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var u = edge[0];
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var v = edge[1];
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var w = edge[2];
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if (distance[u] + w < distance[v]) {
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print_string("Negative cycle detected! Distances are invalid\n");
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}
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}
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return distance;
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}
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int program(int argc, string[] argv) {
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var n = 6;
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var m = 9;
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var edges = new int[][]{ new int[]{0, 1, 4},
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new int[]{0, 2, -3},
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new int[]{2, 1, -2},
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new int[]{2, 3, 10},
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new int[]{3, 1, 6},
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new int[]{2, 4, 1},
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new int[]{2, 5, -9},
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new int[]{3, 5, -1},
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new int[]{5, 4, 4} };
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var source = 0;
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var dest = 5;
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var shortest_path = -12;
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var distance = bellman_ford(n, m, edges, source);
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if (distance[dest] == shortest_path) {
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return 0;
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}
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return 1;
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}
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