implemented Bellmann Ford

Author: JakubSchwenkbeck

src/main/scala/algorithms/graph/BellmannFord.scala

@@ -0,0 +1,30 @@
+package algorithms.graph
+
+import datastructures.graph.Graph
+import scala.collection.mutable
+
+def bellmanford[T](graph: Graph[T], start: T): (mutable.Map[T, Int], Boolean) = {
+  val distances = mutable.Map[T, Int]().withDefaultValue(Int.MaxValue)
+  val pi = mutable.Map[T, T]()
+
+  distances(start) = 0
+
+  for (vertex <- graph.adjacencyList.keys.toList) {
+    if vertex != start then distances(vertex) = Int.MaxValue
+  }
+  for (i <- 1 until graph.adjacencyList.keys.toList.length) {
+    for (edge <- graph.edges) {
+      if (distances(edge.dest) > distances(edge.src) + edge.weight.toInt) {
+        distances(edge.dest) = distances(edge.src) + edge.weight.toInt
+        pi(edge.dest) = edge.src
+      }
+    }
+  }
+  for (edge <- graph.edges) {
+    if (distances(edge.dest) > distances(edge.src) + edge.weight.toInt) {
+      return (distances, false)
+    }
+  }
+
+  (distances, true)
+}

src/main/scala/algorithms/graph/Dijkstra.scala

@@ -9,7 +9,7 @@ import scala.collection.mutable
 /// Uses a priority queue-based approach
 /// Runs in O((V + E) log V) time complexity
 
-def dijkstra[T](graph: Graph[T], start: T): Unit = {
+def dijkstra[T](graph: Graph[T], start: T): Map[T, Int] = {
   val distances = mutable.Map[T, Int]().withDefaultValue(Int.MaxValue)
   val visited = mutable.Set[T]()
   val priorityQueue = PriorityQueue[(T, Int)]()(Ordering.by(-_._2))