66 lines
1.5 KiB
Java
66 lines
1.5 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(V^2)
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public class Dijkstra {
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public static void shortestPaths(List<Edge>[] graph, int s, int[] prio, int[] pred) {
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int n = graph.length;
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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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boolean[] visited = new boolean[n];
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for (int i = 0; i < n; i++) {
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int u = -1;
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for (int j = 0; j < n; j++) {
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if (!visited[j] && (u == -1 || prio[u] > prio[j]))
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u = j;
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}
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if (prio[u] == Integer.MAX_VALUE)
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break;
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visited[u] = true;
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for (Edge e : graph[u]) {
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int v = e.t;
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int nprio = prio[u] + e.cost;
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if (prio[v] > nprio) {
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prio[v] = nprio;
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pred[v] = u;
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}
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}
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}
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}
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static class Edge {
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int t, 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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