63 lines
1.6 KiB
Java
63 lines
1.6 KiB
Java
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import java.util.*;
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import java.util.stream.Stream;
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// https://en.wikipedia.org/wiki/Dijkstra's_algorithm in O(E*log(V))
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public class DijkstraHeap {
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public static void shortestPaths(List<Edge>[] edges, int s, int[] prio, int[] pred) {
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Arrays.fill(pred, -1);
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Arrays.fill(prio, Integer.MAX_VALUE);
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prio[s] = 0;
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PriorityQueue<Long> q = new PriorityQueue<>();
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q.add((long) s);
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while (!q.isEmpty()) {
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long cur = q.remove();
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int curu = (int) cur;
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if (cur >>> 32 != prio[curu])
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continue;
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for (Edge e : edges[curu]) {
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int v = e.t;
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int nprio = prio[curu] + e.cost;
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if (prio[v] > nprio) {
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prio[v] = nprio;
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pred[v] = curu;
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q.add(((long) nprio << 32) + v);
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}
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}
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}
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}
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public static class Edge {
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int t;
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int cost;
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public Edge(int t, int cost) {
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this.t = t;
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this.cost = cost;
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}
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}
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// Usage example
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public static void main(String[] args) {
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int[][] cost = { { 0, 3, 2 }, { 0, 0, -2 }, { 0, 0, 0 } };
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int n = cost.length;
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List<Edge>[] graph = Stream.generate(ArrayList::new).limit(n).toArray(List[]::new);
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for (int i = 0; i < n; i++) {
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for (int j = 0; j < n; j++) {
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if (cost[i][j] != 0) {
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graph[i].add(new Edge(j, cost[i][j]));
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}
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}
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}
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int[] dist = new int[n];
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int[] pred = new int[n];
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shortestPaths(graph, 0, dist, pred);
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System.out.println(0 == dist[0]);
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System.out.println(3 == dist[1]);
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System.out.println(1 == dist[2]);
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System.out.println(-1 == pred[0]);
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System.out.println(0 == pred[1]);
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System.out.println(1 == pred[2]);
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}
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}
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