package eliminateCodeFear.algorithms.graphs.dijsktra;

class ShortestPath {

    static final int V = 9; // No. of vertices

    // A utility function to find the vertex with minimum distance value,
    // from the set of vertices not yet included in shortest path tree
    int nextMinDistance(int dist[], Boolean sptSet[]) {
        // Initialize min value
        int min = Integer.MAX_VALUE, min_index = -1;

        for (int v = 0; v < V; v++)
            if (sptSet[v] == false && dist[v] <= min) {
                min = dist[v];
                min_index = v;
            }

        return min_index;
    }

    // Function that implements Dijkstra's single source shortest path
    // algorithm for a graph represented using adjacency matrix
    // representation
    void dijkstra(int graph[][], int src) {

        // The output array. dist[i] will hold
        // the shortest distance from src to i
        int dist[] = new int[V];

        // sptSet[i] will true if vertex i is included in shortest
        // path tree or shortest distance from src to i is finalized
        Boolean sptSet[] = new Boolean[V];

        // Initialize all distances as INFINITE and stpSet[] as false
        for (int i = 0; i < V; i++) {
            dist[i] = Integer.MAX_VALUE;
            sptSet[i] = false;
        }

        // Distance of source vertex from itself is always 0
        dist[src] = 0;

        // Find shortest path for all vertices
        for (int count = 0; count < V - 1; count++) {
            // Pick the minimum distance vertex from the set of vertices
            // not yet processed. u is always equal to src in first
            // iteration.
            int u = nextMinDistance(dist, sptSet);
            System.out.println("Next min u = " + u);

            // Mark the picked vertex as processed
            sptSet[u] = true;

            // Update dist value of the adjacent vertices of the
            // picked vertex.
            for (int v = 0; v < V; v++) {
                System.out.println("v = " + v);
                // Update dist[v] only if is not in sptSet, there is an
                // edge from u to v, and total weight of path from src to
                // v through u is smaller than current value of dist[v]
                if (!sptSet[v] && graph[u][v] != 0 &&
                        dist[u] != Integer.MAX_VALUE &&
                        dist[u] + graph[u][v] < dist[v]) {
                    int newDistance = dist[u] + graph[u][v];
                    System.out.println("Shortest path to dist[" + v + "] = " + dist[u] + " + " + graph[u][v] + " = " + newDistance);
                    dist[v] = dist[u] + graph[u][v];
                }
            }
        }

        // print the constructed distance array
        printSolution(dist, V);
    }

    // A utility function to print the constructed distance array
    void printSolution(int dist[], int n) {
        System.out.println("Vertex   Distance from Source");
        for (int i = 0; i < V; i++)
            System.out.println(i + " \t\t " + dist[i]);
    }

    // based on https://www.geeksforgeeks.org/greedy-algorithms-set-6-dijkstras-shortest-path-algorithm/
}
