Graph - 그래프

용어

• vortex = node
• edge = connection (mostly bi-directional)
• vortex의 plural형 = vertices

함수 구현

import java.util.ArrayList;
import java.util.HashMap;

public class Graphs {
	// adjList
	private HashMap<String, ArrayList<String>> adjList = new HashMap<>();
	
	public void printGraph() {
		System.out.println(adjList);
	}
	
	public boolean addVertex(String vertex) {
		// hashmap : we can't have duplicates
		// so we should have some code to make sure the value we're using for our vertex
		// isn't already in our hashmap.
		if (adjList.get(vertex) == null) {
			adjList.put(vertex, new ArrayList<String>());
			return true;
		}
		
		return false;
	}
	
	public boolean addEdge(String vertex1, String vertex2) {
		if(adjList.get(vertex1)!=null && adjList.get(vertex2)!=null) {
			adjList.get(vertex1).add(vertex2);
			adjList.get(vertex2).add(vertex1);
			return true;
		}
		return false;
	}

	public boolean removeEdge(String vertex1, String vertex2) {
		if(adjList.get(vertex1)!=null && adjList.get(vertex2)!=null) {
			adjList.get(vertex1).remove(vertex2);
			adjList.get(vertex2).remove(vertex1);
			return true;
		}
		return false;
	}
	
	public boolean removeVertex(String vertex) {
		if(adjList.get(vertex) == null) return false;
		// 해당 vertex가 그래프 안에 없음
		
		for(String otherVertex : adjList.get(vertex)) {
			adjList.get(otherVertex).remove(vertex);
		}
		adjList.remove(vertex);
		return true;
	}
}

Main 실행 부분

public class Main {

	public static void main(String[] args) {
		
		Graphs myGraph = new Graphs();
		myGraph.addVertex("A");
		myGraph.addVertex("B");
		myGraph.addVertex("C");
		myGraph.addVertex("D");
		myGraph.addEdge("A", "B");
		myGraph.addEdge("A", "C");
		myGraph.addEdge("B", "D");
		myGraph.addEdge("D", "C");
		myGraph.addEdge("A", "D");
		myGraph.printGraph();
		
		myGraph.removeEdge("A", "B");
		myGraph.printGraph();
		myGraph.removeEdge("C", "B");
		myGraph.printGraph();
		
		myGraph.removeVertex("D");
		myGraph.printGraph();

	}

}

결과 :