Mauritus national flag problem

Question

I\'ve made a solution for the Dutch national flag problem already.

But this time, I want to try something more difficult: the Mauritus national flag problem - 4 colours,

Answer 1

Basically, maintain the following :

a[0-p] => '0'
a[p-q] => '1'
a[q-r] => '2'
a[r-s] => traversing! 
a[s-length] => '3'          

Code:

        int p=-1,q=-1,r=0,s=a.length-1;
        while(r<=s){
            if(a[r]==0){
                exchange(a,p+1,r);
                p++;r++;
                if(q!=-1)
                    q++;
            } else if (a[r]==1){
                if(q==-1)
                    q=p;
                exchange(a,q+1,r);
                q++;r++;
            } else if(a[r]==2) {
                r++;
            } else {
                exchange(a,r,s);
                s--;
            }

        }