Check the graph is Eulerian, Semi-Eulerian or Non-Eulerian.

CheckEulerian.java

/**
 * @param adjacencyList of the graph
 * @return ArrayList of oddVertices. if oddVertices is empty its Eulerian,
 * if it has 2 elements its Semi-Eulerian, else its not Eulerian.
 */
public <P extends Integer, Q extends ArrayList<P>> ArrayList<P> checkEulerian(HashMap<P, Q> adjacencyList) {
    ArrayList<P> oddVertices = new ArrayList<P>();
    Iterator iterator = adjacencyList.keySet().iterator();
    while(iterator.hasNext()) {
        P key = (P) iterator.next();
        int checkEven=adjacencyList.get(key).size()%2;
        if(checkEven!=0) {
            oddVertices.add(key);
        }
    }
    return oddVertices;
}