public String toString(){
        StringBuilder sb = new StringBuilder();
        String NEWLINE = System.getProperty("line.separator");
        
        sb.append("\tV: " + this.V + "\tE: " + this.E + NEWLINE);
        
        sb.append("   ");
        for(int v = 0 ; v < this.V; v++){
            sb.append(String.format("%3d", v));
        }
        sb.append(NEWLINE);
        
        for(int v = 0; v < this.V; v++){
            sb.append(String.format("%3d", v));
            for(int w = 0; w < this.V; w++){
                if(this.matrix[v][w]) sb.append("  T");
                else sb.append("   ");
            }
            sb.append(NEWLINE);
        }
        sb.append(NEWLINE);
        
        return sb.toString();
    }