79 lines
1.8 KiB
Java
79 lines
1.8 KiB
Java
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import java.util.*;
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import java.util.stream.Stream;
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public class DijkstraSegmentTree {
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public static void shortestPaths(List<Edge>[] edges, int s, long[] prio, int[] pred) {
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Arrays.fill(pred, -1);
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Arrays.fill(prio, Long.MAX_VALUE);
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prio[s] = 0;
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long[] t = new long[edges.length * 2];
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Arrays.fill(t, Long.MAX_VALUE);
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set(t, s, 0);
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while (true) {
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int cur = minIndex(t);
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if (t[cur + t.length / 2] == Long.MAX_VALUE)
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break;
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set(t, cur, Long.MAX_VALUE);
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for (Edge e : edges[cur]) {
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int v = e.t;
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long nprio = prio[cur] + e.cost;
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if (prio[v] > nprio) {
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prio[v] = nprio;
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pred[v] = cur;
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set(t, v, nprio);
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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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static void set(long[] t, int i, long value) {
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i += t.length / 2;
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if (t[i] < value && value != Long.MAX_VALUE)
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return;
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t[i] = value;
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for (; i > 1; i >>= 1)
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t[i >> 1] = Math.min(t[i], t[i ^ 1]);
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}
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static int minIndex(long[] t) {
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int res = 1;
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while (res < t.length / 2)
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res = res * 2 + (t[res * 2] > t[1] ? 1 : 0);
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return res - t.length / 2;
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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>[] edges = 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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edges[i].add(new Edge(j, cost[i][j]));
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}
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}
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}
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long[] dist = new long[n];
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int[] pred = new int[n];
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shortestPaths(edges, 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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