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Dijkstra’s Shortest Path Algorithm
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Dijkstra’s Shortest Path Algorithm
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// A Java program for Dijkstra's single source shortest path
// algorithm. The program is for adjacency matrix
// representation of the graph
import java.io.*;
import java.lang.*;
import java.util.*;
class ShortestPath {
// A utility function to find the vertex with minimum
// distance value, from the set of vertices not yet
// included in shortest path tree
static final int V = 9;
int minDistance(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;
}
// A utility function to print the constructed distance
// array
void printSolution(int dist[])
{
System.out.println(
"Vertex \t\t Distance from Source");
for (int i = 0; i < V; i++)
System.out.println(i + " \t\t " + dist[i]);
}
// Function that implements Dijkstra's single source
// shortest path algorithm for a graph represented using
// adjacency matrix representation
void dijkstra(int graph[][], int src)
{
int dist[] = new int[V]; // The output array.
// dist[i] will hold
// the shortest distance from src to i
// 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 = minDistance(dist, sptSet);
// 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++)
// 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])
dist[v] = dist[u] + graph[u][v];
}
// print the constructed distance array
printSolution(dist);
}
// Driver's code
public static void main(String[] args)
{
/* Let us create the example graph discussed above
*/
int graph[][]
= new int[][] { { 0, 4, 0, 0, 0, 0, 0, 8, 0 },
{ 4, 0, 8, 0, 0, 0, 0, 11, 0 },
{ 0, 8, 0, 7, 0, 4, 0, 0, 2 },
{ 0, 0, 7, 0, 9, 14, 0, 0, 0 },
{ 0, 0, 0, 9, 0, 10, 0, 0, 0 },
{ 0, 0, 4, 14, 10, 0, 2, 0, 0 },
{ 0, 0, 0, 0, 0, 2, 0, 1, 6 },
{ 8, 11, 0, 0, 0, 0, 1, 0, 7 },
{ 0, 0, 2, 0, 0, 0, 6, 7, 0 } };
ShortestPath t = new ShortestPath();
// Function call
t.dijkstra(graph, 0);
}
}