Added Dijkstra Algorithm

Shortest-Path-Algorithms/dijkstra_algorithm.go

@@ -0,0 +1,183 @@
+//Program in Go to implement Djikstra's Algorithm
+package main
+
+import "fmt"
+
+type Edge struct {
+	first_node_id int;
+	second_node_id int;
+	edge_length int;
+}
+
+type Graph struct {
+	edges []Edge;
+	nodes []Node;
+}
+
+type Node struct {
+	id int;
+	temp_val int;
+	temp_path []int;
+}
+
+//Takes an input graph, starting node.id, ending node.id
+func shortest_path(graph Graph, start int, end int) int {
+	unvisited_nodes := graph.nodes
+	var visited_nodes []Node
+
+	start_node := Node{start, 0, []int{start}}
+	//Start with input start node
+	visited_nodes = append(visited_nodes, start_node)
+	unvisited_nodes = remove(unvisited_nodes, start_node.id)
+	end_flag := false
+	new_neighbors := update_neighbors(graph,visited_nodes)
+	minimum := -1
+	for end_flag == false {
+		minimum = -1
+		new_neighbors = update_neighbors(graph,visited_nodes)
+		unvisited_nodes = update_unvisited_nodes(unvisited_nodes, new_neighbors)
+		//Choose New node to visit
+		for _, node := range new_neighbors {
+			if minimum == -1 {
+				minimum = node.temp_val
+				start_node = node
+			}else if minimum > node.temp_val{
+				minimum = node.temp_val
+				start_node = node
+			}
+		}
+		visited_nodes = append(visited_nodes, start_node)
+		unvisited_nodes = remove(unvisited_nodes, start_node.id)
+		if start_node.id == end {
+			end_flag = true
+		}
+	}
+	//And thus the start node has become the end node
+	//fmt.Println(start_node.temp_path)
+	return start_node.temp_val
+}
+
+func remove(slice []Node, s int) []Node {
+	var my_index int
+	for index, element := range slice {
+		if element.id == s {
+			my_index = index
+		}
+	}
+    return append(slice[:my_index], slice[my_index+1:]...)
+}
+
+//Takes input Nodes and calculates all nieghbors and distances
+func update_neighbors(graph Graph, start_nodes []Node) []Node {
+	var neighbors []Node
+	for _, start := range start_nodes{
+		my_neighbors := get_neighbors(graph,start, start_nodes)
+		//Update Neighbor Values
+		for index, element := range my_neighbors {
+			my_neighbors[index].temp_val = element.temp_val + start.temp_val
+			my_neighbors[index].temp_path = append(my_neighbors[index].temp_path, my_neighbors[index].id)
+		}
+		//Compare to all neighbors
+		for _, neigh := range my_neighbors {
+			found := false
+			for aindex, aneigh := range neighbors {
+				if neigh.id == aneigh.id {
+					found = true
+					if neigh.temp_val < aneigh.temp_val {
+						neighbors[aindex].temp_val = neigh.temp_val
+						neighbors[aindex].temp_path = neigh.temp_path
+					}
+				}
+			}
+			if found == false {
+				neighbors = append(neighbors, neigh)
+			}
+		}
+	}
+	return neighbors
+}
+
+//Takes input unvisited_nodes and new neighbors and updates their temp values
+func update_unvisited_nodes(unvisited_nodes []Node, new_neighbors []Node) []Node {
+	for index, element := range unvisited_nodes {
+		for _, neighbor := range new_neighbors {
+			if neighbor.id == element.id {
+				if neighbor.temp_val < element.temp_val || element.temp_val == -1 {
+					unvisited_nodes[index].temp_val = neighbor.temp_val
+					unvisited_nodes[index].temp_path = neighbor.temp_path
+				}
+			}
+		}
+	}
+	return unvisited_nodes
+}
+
+//Takes an input Node and calculates distance to immediate neighbors
+func get_neighbors(graph Graph, start Node, visited_nodes []Node) []Node {
+	var neighbors []Node
+	for _, element := range graph.edges {
+		my_first_node_id := element.first_node_id
+		my_second_node_id := element.second_node_id
+		first_node_visited := false
+		second_node_visited := false
+		for _, node := range visited_nodes {
+			if my_first_node_id == node.id {
+				first_node_visited = true
+			}
+			if my_second_node_id == node.id{
+				second_node_visited = true
+			}
+		}
+		if my_first_node_id == start.id && second_node_visited == false {
+			found := false
+			for _, element2 := range neighbors {
+				if element2.id == my_second_node_id {
+					found = true
+				}
+			}
+			if found != true {
+				neighbors = append(neighbors, Node{my_second_node_id,element.edge_length,start.temp_path})
+			}
+		}
+		if my_second_node_id == start.id && first_node_visited == false{
+			found := false
+			for _, element2 := range neighbors {
+				if element2.id == my_first_node_id {
+					found = true
+				}
+			}
+			if found != true {
+				neighbors = append(neighbors, Node{my_first_node_id,element.edge_length,start.temp_path})
+			}
+		}
+	}
+	return neighbors
+}
+
+func main() {
+	var edges_list []Edge
+	edge_1_to_2 := Edge{1, 2, 1}
+	edge_2_to_3 := Edge{2, 3, 5}
+	edge_1_to_3 := Edge{1, 3, 5}
+	edge_2_to_4 := Edge{2, 4, 1}
+	edge_2_to_5 := Edge{2, 5, 5}
+	edge_3_to_4 := Edge{3, 4, 5}
+	edge_4_to_5 := Edge{4, 5, 5}
+	edges_list = append(edges_list, edge_1_to_2)
+	edges_list = append(edges_list, edge_2_to_3)
+	edges_list = append(edges_list, edge_1_to_3)
+	edges_list = append(edges_list, edge_2_to_4)
+	edges_list = append(edges_list, edge_2_to_5)
+	edges_list = append(edges_list, edge_3_to_4)
+	edges_list = append(edges_list, edge_4_to_5)
+	//fmt.Println(edges_list)
+	var node_list []Node
+	node_list = append(node_list, Node{1,-1,[]int{0}})
+	node_list = append(node_list, Node{2,-1,[]int{0}})
+	node_list = append(node_list, Node{3,-1,[]int{0}})
+	node_list = append(node_list, Node{4,-1,[]int{0}})
+	node_list = append(node_list, Node{5,-1,[]int{0}})
+	graph := Graph{edges_list, node_list}
+	//fmt.Println(graph)
+	fmt.Println(shortest_path(graph,1,5))
+}