UVa 10356 - Rough Roads

UV 10356 - Rough Roads

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Summary
Dijkstra algorithm

Explanation
1) Dijkstra algorithm after some adjustment of a graph. 2) Create such a graph that for every junction(vertex) will create a vertex from which is a street taken with a bike taken on his back and another vertex which from is street taken riding a bike 3) Run dijkstra - Dijkstra(start, end) with Dijkstra(V0, Vn-1) 4) Hint: Vertexes(junctions) v(0)...v(n-1) are for vertexes from which is bike taken on his back v(n)...v(2n-1) are for vertexes from which is bike ridden 5) For every path from v(a)<--->v(b) create 4 paths in a graph                                 v(a)->v(b+n)                                  v(b+n)->v(a)                                  v(b)->v(a+n)                                  v(a+n)->v(b)

Solution
import java.util.*; import java.io.*;

class Main { public static void main(String[] args) throws Exception { Scanner in = new Scanner(System.in); PrintWriter out = new PrintWriter(System.out, true); int set = 0; while (in.hasNextInt) { set++; out.println("Set #" + set);

int n = in.nextInt; int m = in.nextInt;

List nodeList = new ArrayList; for (int i = 0; i < 2 * n; i++) { Node node = new Node(i); nodeList.add(node); }

for (int i = 0; i < m; i++) { int a = in.nextInt; int b = in.nextInt; int c = in.nextInt;

Node nodeA = nodeList.get(a); Node nodeAN = nodeList.get(a + n); Node nodeB = nodeList.get(b); Node nodeBN = nodeList.get(b + n);

Edge e1 = new Edge(nodeA, nodeBN, c); Edge e2 = new Edge(nodeBN, nodeA, c); Edge e3 = new Edge(nodeAN, nodeB, c); Edge e4 = new Edge(nodeB, nodeAN, c);

nodeA.addEdge(e1); nodeBN.addEdge(e2); nodeAN.addEdge(e3); nodeB.addEdge(e4); }

PriorityQueue queue = new PriorityQueue(2*n, new NodeComparator); Node startNode = nodeList.get(0); startNode.setCurrentCost(0);

queue.add(startNode); for (int i = 1; i < 2 * n; i++) { queue.add(nodeList.get(i)); }

while (!queue.isEmpty) { Node currentNode = queue.remove; List edges = currentNode.getEdges; for (int i = 0; i < edges.size; i++) { Edge e = edges.get(i);

Node start = e.getStart; Node end = e.getEnd; int cost = e.getCost;

// relaxation if (start.getCurrentCost != -1 && (end.getCurrentCost == -1 || (end.getCurrentCost > start.getCurrentCost + cost))) { queue.remove(end); end.setCurrentCost(start.getCurrentCost + cost); end.setPreviousNode(start); queue.add(end); }				}			}

Node target = nodeList.get(n - 1); int currentCost = target.getCurrentCost; if (currentCost == -1) { out.println("?"); } else { out.println(currentCost); }		}

out.flush; out.close;

} }

class Edge { private Node start; private Node end; private int cost;

public Edge(Node start, Node end, int cost) { this.start = start; this.end = end; this.cost = cost; }

public Node getStart { return start; }

public Node getEnd { return end; }

public int getCost { return cost; } }

class Node { private int n;	private List edges = new ArrayList;

private int currentCost = -1; private Node previousNode;

public Node(int n) { this.n = n;	}

public void addEdge(Edge e) { edges.add(e); }

public List getEdges { return edges; }

public int getCurrentCost { return currentCost; }

public void setCurrentCost(int currentCost) { this.currentCost = currentCost; }

public Node getPreviousNode { return previousNode; }

public void setPreviousNode(Node previousNode) { this.previousNode = previousNode; }

@Override public int hashCode { final int prime = 31; int result = 1; result = prime * result + n;		return result; }

@Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass != obj.getClass) return false; Node other = (Node) obj; if (n != other.n)			return false; return true; }

}

class NodeComparator implements Comparator {

public int compare(Node o1, Node o2) { if (o1.getCurrentCost == o2.getCurrentCost) { return 0; } else if (o1.getCurrentCost == -1) { return 1; } else if (o2.getCurrentCost == -1) { return -1; } else if (o1.getCurrentCost < o2.getCurrentCost) { return -1; } else if (o1.getCurrentCost > o2.getCurrentCost) { return 1; }		return 0; }

}