greenTicket challenge

Hi,
I am working on below challenge
http://codingbat.com/prob/p120633
I tried my code as below
public int greenTicket(int a, int b, int c) {

if((a!=b)&&(b!=c))
{
return 0;
}

else{

if((a==b)&&(b==c)&&(c==a)){
return 20;
}

else if((a==b)||(b==c)){
return 10;
}
else{
return 0;
}//inner else close



} //outer else close


}//method close


I am getting below result

Expected      Run            
greenTicket(1, 2, 3) → 0      0      OK         
greenTicket(2, 2, 2) → 20      20      OK         
greenTicket(1, 1, 2) → 10      10      OK         
greenTicket(2, 1, 1) → 10      10      OK         
greenTicket(1, 2, 1) → 10      0      X         
greenTicket(3, 2, 1) → 0      0      OK         
greenTicket(0, 0, 0) → 20      20      OK         
greenTicket(2, 0, 0) → 10      10      OK         
greenTicket(0, 9, 10) → 0      0      OK         
greenTicket(0, 10, 0) → 10      0      X         
greenTicket(9, 9, 9) → 20      20      OK         
greenTicket(9, 0, 9) → 10      0      X         
other tests
X         

how to  improve my approach, results and design of this challenge. How do i make a graphical venn or flow chart or some other relevant diagram to design it before writing code to decide best strategy?
 Please advise