programming-examples/java/Data_Structures/DijkstraSegmentTree.java

import java.util.*;
import java.util.stream.Stream;

public class DijkstraSegmentTree {

	public static void shortestPaths(List<Edge>[] edges, int s, long[] prio, int[] pred) {
		Arrays.fill(pred, -1);
		Arrays.fill(prio, Long.MAX_VALUE);
		prio[s] = 0;
		long[] t = new long[edges.length * 2];
		Arrays.fill(t, Long.MAX_VALUE);
		set(t, s, 0);
		while (true) {
			int cur = minIndex(t);
			if (t[cur + t.length / 2] == Long.MAX_VALUE)
				break;
			set(t, cur, Long.MAX_VALUE);
			for (Edge e : edges[cur]) {
				int v = e.t;
				long nprio = prio[cur] + e.cost;
				if (prio[v] > nprio) {
					prio[v] = nprio;
					pred[v] = cur;
					set(t, v, nprio);
				}
			}
		}
	}

	public static class Edge {
		int t;
		int cost;

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

	static void set(long[] t, int i, long value) {
		i += t.length / 2;
		if (t[i] < value && value != Long.MAX_VALUE)
			return;
		t[i] = value;
		for (; i > 1; i >>= 1)
			t[i >> 1] = Math.min(t[i], t[i ^ 1]);
	}

	static int minIndex(long[] t) {
		int res = 1;
		while (res < t.length / 2)
			res = res * 2 + (t[res * 2] > t[1] ? 1 : 0);
		return res - t.length / 2;
	}

	// Usage example
	public static void main(String[] args) {
		int[][] cost = {{0, 3, 2}, {0, 0, -2}, {0, 0, 0}};
		int n = cost.length;
		List<Edge>[] edges = Stream.generate(ArrayList::new).limit(n).toArray(List[]::new);
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < n; j++) {
				if (cost[i][j] != 0) {
					edges[i].add(new Edge(j, cost[i][j]));
				}
			}
		}
		long[] dist = new long[n];
		int[] pred = new int[n];
		shortestPaths(edges, 0, dist, pred);
		System.out.println(0 == dist[0]);
		System.out.println(3 == dist[1]);
		System.out.println(1 == dist[2]);
		System.out.println(-1 == pred[0]);
		System.out.println(0 == pred[1]);
		System.out.println(1 == pred[2]);
	}
}