add dijkstra to golang (#149)

07_dijkstras_algorithm/golang/01_dijkstras_algorithm.go

@@ -0,0 +1,94 @@
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+var graph map[string]map[string]float64
+var costs map[string]float64
+var parents map[string]string
+var processed []string
+
+func main() {
+	// the graph
+	graph = make(map[string]map[string]float64)
+	graph["start"] = make(map[string]float64)
+	graph["start"]["a"] = 6
+	graph["start"]["b"] = 2
+
+	graph["a"] = make(map[string]float64)
+	graph["a"]["fin"] = 1
+
+	graph["b"] = make(map[string]float64)
+	graph["b"]["a"] = 3
+	graph["b"]["fin"] = 5
+
+	graph["fin"] = make(map[string]float64)
+
+	// the costs table
+	costs = make(map[string]float64)
+	costs["a"] = 6
+	costs["b"] = 2
+	costs["fin"] = math.Inf(1)
+
+	// the parents table
+	parents = make(map[string]string)
+	parents["a"] = "start"
+	parents["b"] = "start"
+	parents["fin"] = ""
+
+	// Find the lowest-cost node that you haven't processed yet.
+	node := find_lowest_cost_node(costs)
+	// If you've processed all the nodes, this while loop is done.
+
+	for node != "" {
+		cost := costs[node]
+		// Go through all the neighbors of this node.
+		neighbors := graph[node]
+
+		for node, _ := range neighbors {
+			new_cost := cost + neighbors[node]
+			// If it's cheaper to get to this neighbor by going through this node...
+			if costs[node] > new_cost {
+				// ... update the cost for this node.
+				costs[node] = new_cost
+				// This node becomes the new parent for this neighbor.
+				parents[node] = node
+			}
+		}
+		// Mark the node as processed.
+		processed = append(processed, node)
+		// Find the next node to process, and loop.
+		node = find_lowest_cost_node(costs)
+	}
+
+	fmt.Println(costs)
+
+}
+
+func find_lowest_cost_node(costs map[string]float64) string {
+	lowest_cost := math.Inf(1)
+	lowest_cost_node := ""
+
+	for node, _ := range costs {
+		// fmt.Println("Node:", node, "Value:", value)
+		cost := costs[node]
+		// If it's the lowest cost so far and hasn't been processed yet...
+		if cost < lowest_cost && !contains(processed, node) {
+			// ... set it as the new lowest-cost node.
+			lowest_cost = cost
+			lowest_cost_node = node
+		}
+	}
+	return lowest_cost_node
+}
+
+func contains(s []string, e string) bool {
+	for _, a := range s {
+		if a == e {
+			return true
+		}
+	}
+	return false
+}