Cod sursa(job #2230074)

Utilizator radustn92Radu Stancu radustn92 Data 9 august 2018 01:50:16
Problema Algoritmul lui Dijkstra Scor 80
Compilator java Status done
Runda Arhiva educationala Marime 6.76 kb
import java.io.*;
import java.util.*;

public class Main {

    public static void main(String[] args) throws IOException {
        InputStream inputStream = new FileInputStream("dijkstra.in");
        OutputStream outputStream = new FileOutputStream("dijkstra.out");

        try (InputReader inputReader = new InputReader(inputStream);
            PrintWriter printWriter = new PrintWriter(outputStream)) {
            int numberNodes = inputReader.nextInt();
            int numberEdges = inputReader.nextInt();
            Graph graph = new Graph(numberNodes);
            for (int edge = 0; edge < numberEdges; edge++) {
                int from = inputReader.nextInt();
                int to = inputReader.nextInt();
                int cost = inputReader.nextInt();
                graph.addEdge(from, to, cost);
            }

            int[] distancesFromNodeOne = Dijkstra.runFromNode(1, graph);
            for (int i = 2; i <= numberNodes; i++) {
                printWriter.print(distancesFromNodeOne[i] + " ");
            }
        }
    }

    static class Dijkstra {

        private static final Integer INF = Integer.MAX_VALUE >> 1;

        public static int[] runFromNode(int source, Graph graph) {
            Heap minHeap = new Heap(graph.getNumberOfNodes());
            minHeap.update(source, 0);
            // only simple paths make sense. they can have length at most N - 1
            for (int totalSteps = 1; totalSteps < graph.getNumberOfNodes(); totalSteps++) {
                int bestNode = minHeap.poll();
                int currNodeCost = minHeap.getCostForNode(bestNode);
                for (Graph.Edge edge : graph.getEdges(bestNode)) {
                    int newEstimate = currNodeCost + edge.cost;
                    if (minHeap.getCostForNode(edge.to) > newEstimate) {
                        minHeap.update(edge.to, newEstimate);
                    }
                }
            }

            int[] costToNode = minHeap.getCostPerNodes();

            // map unreachable nodes to 0 (required by the caller)
            for (int i = 1; i <= graph.getNumberOfNodes(); i++) {
                if (costToNode[i] == INF) {
                    costToNode[i] = 0;
                }
            }

            return costToNode;
        }
    }

    static class Heap {

        private int N;

        private int[] heapOrderedByNode;

        private int[] costPerNode;

        private int[] posForNodeInHeap;

        public Heap(int N) {
            this.N = N;
            this.costPerNode = new int[N + 1];
            this.posForNodeInHeap = new int[N + 1];

            Arrays.fill(costPerNode, Dijkstra.INF);
            heapOrderedByNode = new int[N + 1];
            for (int node = 1; node <= N; node++) {
                heapOrderedByNode[node] = node;
                posForNodeInHeap[node] = node;
                costPerNode[node] = Dijkstra.INF;
            }
        }

        public int poll() {
            int rootNode = heapOrderedByNode[1];
            swapPositions(1, N);
            N--;
            updateDownstream(1);

            return rootNode;
        }

        public int getCostForNode(int node) {
            return costPerNode[node];
        }

        public boolean cmpPositions(int firstPos, int secondPos) {
            return costPerNode[heapOrderedByNode[firstPos]] < costPerNode[heapOrderedByNode[secondPos]];
        }

        public void swap(int[] arr, int pos1, int pos2) {
            int aux = arr[pos1];
            arr[pos1] = arr[pos2];
            arr[pos2] = aux;
        }

        public void swapPositions(int firstPos, int secondPos) {
            posForNodeInHeap[heapOrderedByNode[firstPos]] = secondPos;
            posForNodeInHeap[heapOrderedByNode[secondPos]] = firstPos;
            swap(heapOrderedByNode, firstPos, secondPos);
        }

        private void updateUpstream(int pos) {
            if (pos <= 1) {
                return ;
            }
            while (pos / 2 >= 1 && cmpPositions(pos, pos / 2)) {
                swapPositions(pos, pos / 2);
                pos /= 2;
            }
        }

        private void updateDownstream(int pos) {
            int bestChild;
            while (2 * pos <= N) {
                bestChild = 2 * pos;
                if (2 * pos + 1 <= N && cmpPositions(2 * pos + 1, bestChild)) {
                    bestChild = 2 * pos + 1;
                }

                if (!cmpPositions(bestChild, pos)) {
                    break;
                }

                swapPositions(pos, bestChild);
                pos = bestChild;
            }
        }

        public void update(int node, int newEstimate) {
            costPerNode[node] = newEstimate;

            int positionInHeap = posForNodeInHeap[node];
            if (positionInHeap > 1 && cmpPositions(positionInHeap, positionInHeap / 2)) {
                updateUpstream(positionInHeap);
            } else {
                updateDownstream(positionInHeap);
            }
        }

        public int[] getCostPerNodes() {
            return costPerNode;
        }
    }

    static class Graph {

        private int N;

        private List<List<Edge>> edges;

        public Graph(int numberOfNodes) {
            this.N = numberOfNodes;
            edges = new ArrayList<>(N + 1);
            for (int node = 0; node <= N; node++) {
                edges.add(new LinkedList<>());
            }
        }

        public void addEdge(int from, int to, int cost) {
            edges.get(from).add(new Edge(to, cost));
        }

        public int getNumberOfNodes() {
            return N;
        }

        public List<Edge> getEdges(int node) {
            return edges.get(node);
        }

        static class Edge {
            private int to;

            private int cost;

            public Edge(int to, int cost) {
                this.to = to;
                this.cost = cost;
            }
        }
    }

    static class InputReader implements AutoCloseable {

        private BufferedReader bufferedReader;

        private StringTokenizer stringTokenizer;

        public InputReader(InputStream inputStream) {
            bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
            stringTokenizer = null;
        }

        private String nextToken() {
            if (stringTokenizer == null || !stringTokenizer.hasMoreTokens()) {
                try {
                    stringTokenizer = new StringTokenizer(bufferedReader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }

            return stringTokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(nextToken());
        }

        @Override
        public void close() throws IOException {
            bufferedReader.close();
        }
    }
}