From 3a50470e3d7ed011b924b27566c908753dd7800d Mon Sep 17 00:00:00 2001
From: Evgeny Samsonov <bitniks@yandex.ru>
Date: Tue, 12 Nov 2019 18:18:00 +0300
Subject: [PATCH] Add dijkstras algorithm in golang (#118)

* Golang dijkstra algorithm

* New line in end of file
---
 .../Golang/01_dijkstras_algorithm.go          | 73 +++++++++++++++++++
 1 file changed, 73 insertions(+)
 create mode 100644 07_dijkstras_algorithm/Golang/01_dijkstras_algorithm.go

diff --git a/07_dijkstras_algorithm/Golang/01_dijkstras_algorithm.go b/07_dijkstras_algorithm/Golang/01_dijkstras_algorithm.go
new file mode 100644
index 0000000..b25fb00
--- /dev/null
+++ b/07_dijkstras_algorithm/Golang/01_dijkstras_algorithm.go
@@ -0,0 +1,73 @@
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+func main() {
+	graph := make(map[string]map[string]int)
+	graph["start"] = map[string]int{}
+	graph["start"]["a"] = 6
+	graph["start"]["b"] = 2
+
+	graph["a"] = map[string]int{}
+	graph["a"]["finish"] = 1
+
+	graph["b"] = map[string]int{}
+	graph["b"]["a"] = 3
+	graph["b"]["finish"] = 5
+
+	graph["finish"] = map[string]int{}
+
+	costs, parents := findShortestPath(graph, "start", "finish")
+	fmt.Println(costs, parents)
+}
+
+// Finds shortest path using dijkstra algorithm
+func findShortestPath(graph map[string]map[string]int, startNode string, finishNode string) (map[string]int, map[string]string)  {
+	costs := make(map[string]int)
+	costs[finishNode] = math.MaxInt32
+
+	parents := make(map[string]string)
+	parents[finishNode] = ""
+
+	processed := make(map[string]bool)
+
+	// Initialization of costs and parents
+	for node, cost := range graph[startNode] {
+		costs[node] = cost
+		parents[node] = startNode
+	}
+
+	lowestCostNode := findLowestCostNode(costs, processed)
+	for ; lowestCostNode != "" ; {
+		// Calculation costs for neighbours
+		for node, cost := range graph[lowestCostNode] {
+			newCost := costs[lowestCostNode] + cost
+			if newCost < costs[node] {
+				// Set new cost for this node
+				costs[node] = newCost
+				parents[node] = lowestCostNode
+			}
+		}
+
+		processed[lowestCostNode] = true
+		lowestCostNode = findLowestCostNode(costs, processed)
+	}
+
+	return costs, parents
+}
+
+func findLowestCostNode(costs map[string]int, processed map[string]bool) string {
+	lowestCost := math.MaxInt32
+	lowestCostNode := ""
+	for node, cost := range costs {
+		if _, inProcessed := processed[node]; cost < lowestCost && !inProcessed {
+			lowestCost = cost
+			lowestCostNode = node
+		}
+	}
+
+	return lowestCostNode
+}