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v/examples/graphs/bfs2.v

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// Author: CCS
// I follow literally code in C, done many years ago
fn main() {
// Adjacency matrix as a map
graph := {
'A': ['B', 'C']
'B': ['A', 'D', 'E']
'C': ['A', 'F']
'D': ['B']
'E': ['B', 'F']
'F': ['C', 'E']
}
println('Graph: ${graph}')
path := breadth_first_search_path(graph, 'A', 'F')
println('\n The shortest path from node A to node F is: ${path.reverse()}')
}
// Breadth-First Search (BFS) allows you to find the shortest distance between two nodes in the graph.
fn breadth_first_search_path(graph map[string][]string, start string, target string) []string {
mut path := []string{} // ONE PATH with SUCCESS = array
mut queue := []string{} // a queue ... many paths
// all_nodes := graph.keys() // get a key of this map
// a map to store all the nodes visited to avoid cycles
// start all them with False, not visited yet
mut visited := visited_init(graph) // a map fully
// false ==> not visited yet: {'A': false, 'B': false, 'C': false, 'D': false, 'E': false}
queue << start // first arrival
for queue.len != 0 {
mut node := departure(mut queue) // get the front node and remove it
if visited[node] == false { // check if this node is already visited
// if no ... test it searchinf for a final node
visited[node] = true // means: visit this node
if node == target {
path = build_path_reverse(graph, start, node, visited)
return path
}
// Expansion of node removed from queue
print('\n Expansion of node ${node} (true/false): ${graph[node]}')
// take all nodes from the node
for vertex in graph[node] { // println("\n ...${vertex}")
// not explored yet
if visited[vertex] == false {
queue << vertex
}
}
print('\n QUEUE: ${queue} (only not visited) \n Visited: ${visited}')
}
}
path = ['Path not found, problem in the Graph, start or end nodes! ']
return path
}
// classical removing of a node from the start of a queue
fn departure(mut queue []string) string {
mut x := queue[0]
queue.delete(0)
return x
}
// 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 temp := map[string]bool{} // attention in these initializations with maps
for i, _ in a_graph {
temp[i] = false
}
return temp
}
// Based in the current node that is final, search for its parent, already visited, up to the root or start node
fn build_path_reverse(graph map[string][]string, start string, final string, visited map[string]bool) []string {
print('\n\n Nodes visited (true) or no (false): ${visited}')
array_of_nodes := graph.keys()
mut current := final
mut path := []string{}
path << current
for (current != start) {
for i in array_of_nodes {
if (current in graph[i]) && (visited[i] == true) {
current = i
break // the first ocurrence is enough
}
}
path << current // update the path tracked
}
return path
}
//======================================================