private void resetColor(Map<String,Boolean> colorsUsed){
        Set<String> colors = new HashSet<String>();
        for(String color : colorsUsed.keySet()){
            colors.add(color);
        }
        for(String color : colors){
            colorsUsed.remove(color);
            colorsUsed.put(color, false);
        }
    }
http://www.geeksforgeeks.org/graph-coloring-set-2-greedy-algorithm/
src/com/interview/graph/GraphColoring.java