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v/examples/graphs/topological_sorting_dfs.v

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