dijkstra priority queue java code example

Example 1: dijkstra implementation with the help of priority queue in python

import heapq


def calculate_distances(graph, starting_vertex):
    distances = {vertex: float('infinity') for vertex in graph}
    distances[starting_vertex] = 0

    pq = [(0, starting_vertex)]
    while len(pq) > 0:
        current_distance, current_vertex = heapq.heappop(pq)

        # Nodes can get added to the priority queue multiple times. We only
        # process a vertex the first time we remove it from the priority queue.
        if current_distance > distances[current_vertex]:
            continue

        for neighbor, weight in graph[current_vertex].items():
            distance = current_distance + weight

            # Only consider this new path if it's better than any path we've
            # already found.
            if distance < distances[neighbor]:
                distances[neighbor] = distance
                heapq.heappush(pq, (distance, neighbor))

    return distances


example_graph = {
    'U': {'V': 2, 'W': 5, 'X': 1},
    'V': {'U': 2, 'X': 2, 'W': 3},
    'W': {'V': 3, 'U': 5, 'X': 3, 'Y': 1, 'Z': 5},
    'X': {'U': 1, 'V': 2, 'W': 3, 'Y': 1},
    'Y': {'X': 1, 'W': 1, 'Z': 1},
    'Z': {'W': 5, 'Y': 1},
}
print(calculate_distances(example_graph, 'X'))
# => {'U': 1, 'W': 2, 'V': 2, 'Y': 1, 'X': 0, 'Z': 2}

Example 2: priority queue in java

import java.util.PriorityQueue;
import java.util.Iterator;

class Main {
    public static void main(String[] args) {

        // Creating a priority queue
        PriorityQueue<Integer> numbers = new PriorityQueue<>();
        numbers.add(4);
        numbers.add(2);
        numbers.add(1);
        System.out.print("PriorityQueue using iterator(): ");

        //Using the iterator() method
        Iterator<Integer> iterate = numbers.iterator();
        while(iterate.hasNext()) {
            System.out.print(iterate.next());
            System.out.print(", ");
        }
    }
}

Example 3: thread priority in java

class TestMultiPriority1 extends Thread{  
 public void run(){  
   System.out.println("running thread name is:"+Thread.currentThread().getName());  
   System.out.println("running thread priority is:"+Thread.currentThread().getPriority());  
  
  }  
 public static void main(String args[]){  
  TestMultiPriority1 m1=new TestMultiPriority1();  
  TestMultiPriority1 m2=new TestMultiPriority1();  
  m1.setPriority(Thread.MIN_PRIORITY);  
  m2.setPriority(Thread.MAX_PRIORITY);  
  m1.start();  
  m2.start();  
   
 }  
}