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91 lines
2.7 KiB
V
91 lines
2.7 KiB
V
// https://en.wikipedia.org/wiki/Topological_sorting
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// A DFS RECURSIVE ALGORITHM ....
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// An alternative algorithm for topological sorting is based on depth-first search. The algorithm loops through each node of the graph, in an arbitrary order, initiating a depth-first search that terminates when it hits any node that has already been visited since the beginning
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// of the topological sort or the node has no outgoing edges (i.e. a leaf node)
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// Discussion: https://www.gatevidyalay.com/topological-sort-topological-sorting/
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// $ v run dfs_topological_ordering.v
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// Author: CCS
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// THE DFS RECURSIVE .... classical searchig for leaves nodes
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// the arguments are used in the function to avoid global variables....
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fn dfs_recursive(u string, mut visited map[string]bool, graph map[string][]string, mut top_sorting []string) {
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print(' Visiting: $u -> ')
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visited[u] = true
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for v in graph[u] {
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if visited[v] == false {
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dfs_recursive(v, mut visited, graph, mut top_sorting)
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}
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}
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top_sorting << u
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}
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// Creating aa map to initialize with of visited nodes .... all with false in the init
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// so these nodes are NOT VISITED YET
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fn visited_init(a_graph map[string][]string) map[string]bool {
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mut array_of_keys := a_graph.keys() // get all keys of this map
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mut temp := map[string]bool{} // attention in these initializations with maps
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for i in array_of_keys {
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temp[i] = false
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}
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return temp
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}
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// attention here a map STRING ---> ONE BOOLEAN ... not a string
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fn main() {
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// A map illustration to use in a graph
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// the graph: adjacency matrix
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graph_01 := {
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'A': ['C', 'B']
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'B': ['D']
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'C': ['D']
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'D': []
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}
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graph_02 := {
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'A': ['B', 'C', 'D']
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'B': ['E']
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'C': ['F']
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'D': ['G']
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'E': ['H']
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'F': ['H']
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'G': ['H']
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'H': [] // no cycles
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}
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// from: https://en.wikipedia.org/wiki/Topological_sorting
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graph_03 := {
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'5': ['11']
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'7': ['11', '8']
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'3': ['8', '10']
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'11': ['2', '9', '10']
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'8': ['9']
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'2': []
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'9': []
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'10': []
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}
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mut graph := map[string][]string{} // the graph: adjacency matrix
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for index, g_value in [graph_01, graph_02, graph_03] {
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println('Topological sorting for the graph $index using a DFS recursive')
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graph = g_value.clone() // graphs_sample[g].clone() // choice your SAMPLE
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// mut n_nodes := graph.len
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mut visited := visited_init(graph) // a map with nodes not visited
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// mut start := (graph.keys()).first() // arbitrary, any node if you wish
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mut top_sorting := []string{}
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// advantages of map ... getting all nodes
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for i in graph.keys() {
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if visited[i] != true {
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dfs_recursive(i, mut visited, graph, mut top_sorting)
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}
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}
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print('\n A topological sorting of graph $index : ')
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// println(g_value)
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println(top_sorting.reverse())
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println('')
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} // End of for
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}
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