diff --git a/Others/Dijkstra.java b/Others/Dijkstra.java deleted file mode 100644 index ae9d35f08..000000000 --- a/Others/Dijkstra.java +++ /dev/null @@ -1,177 +0,0 @@ -package Others; - -/** - * Dijkstra's algorithm,is a graph search algorithm that solves the single-source - * shortest path problem for a graph with nonnegative edge path costs, producing - * a shortest path tree. - * - * NOTE: The inputs to Dijkstra's algorithm are a directed and weighted graph consisting - * of 2 or more nodes, generally represented by an adjacency matrix or list, and a start node. - * - * Original source of code: https://rosettacode.org/wiki/Dijkstra%27s_algorithm#Java - * Also most of the comments are from RosettaCode. - * - */ -//import java.io.*; -import java.util.*; -public class Dijkstra { - private static final Graph.Edge[] GRAPH = { - new Graph.Edge("a", "b", 7), //Distance from node "a" to node "b" is 7. In the current Graph there is no way to move the other way (e,g, from "b" to "a"), a new edge would be needed for that - new Graph.Edge("a", "c", 9), - new Graph.Edge("a", "f", 14), - new Graph.Edge("b", "c", 10), - new Graph.Edge("b", "d", 15), - new Graph.Edge("c", "d", 11), - new Graph.Edge("c", "f", 2), - new Graph.Edge("d", "e", 6), - new Graph.Edge("e", "f", 9), - }; - private static final String START = "a"; - private static final String END = "e"; - - /** - * main function - * Will run the code with "GRAPH" that was defined above. - */ - public static void main(String[] args) { - Graph g = new Graph(GRAPH); - g.dijkstra(START); - g.printPath(END); - //g.printAllPaths(); - } -} - -class Graph { - private final Map graph; // mapping of vertex names to Vertex objects, built from a set of Edges - - /** One edge of the graph (only used by Graph constructor) */ - public static class Edge { - public final String v1, v2; - public final int dist; - public Edge(String v1, String v2, int dist) { - this.v1 = v1; - this.v2 = v2; - this.dist = dist; - } - } - - /** One vertex of the graph, complete with mappings to neighbouring vertices */ - public static class Vertex implements Comparable{ - public final String name; - public int dist = Integer.MAX_VALUE; // MAX_VALUE assumed to be infinity - public Vertex previous = null; - public final Map neighbours = new HashMap<>(); - - public Vertex(String name) - { - this.name = name; - } - - private void printPath() - { - if (this == this.previous) - { - System.out.printf("%s", this.name); - } - else if (this.previous == null) - { - System.out.printf("%s(unreached)", this.name); - } - else - { - this.previous.printPath(); - System.out.printf(" -> %s(%d)", this.name, this.dist); - } - } - - public int compareTo(Vertex other) - { - if (dist == other.dist) - return name.compareTo(other.name); - - return Integer.compare(dist, other.dist); - } - - @Override public String toString() - { - return "(" + name + ", " + dist + ")"; - } -} - - /** Builds a graph from a set of edges */ - public Graph(Edge[] edges) { - graph = new HashMap<>(edges.length); - - //one pass to find all vertices - for (Edge e : edges) { - if (!graph.containsKey(e.v1)) graph.put(e.v1, new Vertex(e.v1)); - if (!graph.containsKey(e.v2)) graph.put(e.v2, new Vertex(e.v2)); - } - - //another pass to set neighbouring vertices - for (Edge e : edges) { - graph.get(e.v1).neighbours.put(graph.get(e.v2), e.dist); - //graph.get(e.v2).neighbours.put(graph.get(e.v1), e.dist); // also do this for an undirected graph - } - } - - /** Runs dijkstra using a specified source vertex */ - public void dijkstra(String startName) { - if (!graph.containsKey(startName)) { - System.err.printf("Graph doesn't contain start vertex \"%s\"\n", startName); - return; - } - final Vertex source = graph.get(startName); - NavigableSet q = new TreeSet<>(); - - // set-up vertices - for (Vertex v : graph.values()) { - v.previous = v == source ? source : null; - v.dist = v == source ? 0 : Integer.MAX_VALUE; - q.add(v); - } - - dijkstra(q); - } - - /** Implementation of dijkstra's algorithm using a binary heap. */ - private void dijkstra(final NavigableSet q) { - Vertex u, v; - while (!q.isEmpty()) { - - u = q.pollFirst(); // vertex with shortest distance (first iteration will return source) - if (u.dist == Integer.MAX_VALUE) break; // we can ignore u (and any other remaining vertices) since they are unreachable - - //look at distances to each neighbour - for (Map.Entry a : u.neighbours.entrySet()) { - v = a.getKey(); //the neighbour in this iteration - - final int alternateDist = u.dist + a.getValue(); - if (alternateDist < v.dist) { // shorter path to neighbour found - q.remove(v); - v.dist = alternateDist; - v.previous = u; - q.add(v); - } - } - } - } - - /** Prints a path from the source to the specified vertex */ - public void printPath(String endName) { - if (!graph.containsKey(endName)) { - System.err.printf("Graph doesn't contain end vertex \"%s\"\n", endName); - return; - } - - graph.get(endName).printPath(); - System.out.println(); - } - /** Prints the path from the source to every vertex (output order is not guaranteed) */ - public void printAllPaths() { - for (Vertex v : graph.values()) { - v.printPath(); - System.out.println(); - } - } -} \ No newline at end of file