Codingame : Teads Sponsored Contest Java

Teads_Sponsored_Contest.java

import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Scanner;
import java.util.Set;
import java.util.stream.Collectors;

class Solution {

	private static class Node {
		
		private final Integer id;
		private final Set<Node> adjacentNodes;
		
		private Node(Integer id) {
			this.id = id;
			this.adjacentNodes = new HashSet<>();
		}
		
		public Integer getId() {
			return id;
		}

		public void addAdjacentNode(Node adjacentNodeId) {
			adjacentNodes.add(adjacentNodeId);
		}
		
		public void removeAdjacentNode(Node adjacentNodeId) {
			adjacentNodes.remove(adjacentNodeId);
		}
		
		public void removeFromAdjacentNodes() {
			adjacentNodes.stream().forEach(adjacentNode -> adjacentNode.removeAdjacentNode(this));
		}
		
		public boolean isLeaf() {
			return adjacentNodes.size() == 1;
		}
		
	}
	
    public static void main(String args[]) {
    	
        Scanner in = new Scanner(System.in);
        int n = in.nextInt(); // the number of adjacency relations
        
        Map<Integer, Node> graph = new HashMap<>();
        for (int i = 0; i < n; i++) {
        	Integer xi = Integer.valueOf(in.nextInt()); // the ID of a person which is adjacent to yi
        	Integer yi = Integer.valueOf(in.nextInt()); // the ID of a person which is adjacent to xi
        	Node xiNode = graph.computeIfAbsent(xi, key -> new Node(key));
        	Node yiNode = graph.computeIfAbsent(yi, key -> new Node(key));
        	xiNode.addAdjacentNode(yiNode);
        	yiNode.addAdjacentNode(xiNode);
        }

        System.out.println(calculateMinimumPropagationSteps(graph)); // The minimal amount of steps required to completely propagate the advertisement
    }

    private static int calculateMinimumPropagationSteps(Map<Integer, Node> graph) {
    	int minimumPropagationSteps = 0;
    	while (graph.size() > 1) {
    		removeLeaves(graph);
    		minimumPropagationSteps++;
    	}
    	return minimumPropagationSteps;
    }
    
    private static void removeLeaves(Map<Integer, Node> graph) {
        //use filter on stream to put in set
    	Set<Node> leaves = graph.values().stream().filter(Node::isLeaf).collect(Collectors.toSet());
    	//use lambda definitions to remove leaves
    	leaves.stream().forEach(leaf -> {
    		graph.remove(leaf.getId());
    		leaf.removeFromAdjacentNodes();
		});
    }
    
}