1573. Number of Ways to Split a String

class Solution {
    public int numWays(String s) {
      int count=0;
        long n=s.length();
        long  d=1000000007;
        for(int i=0;i<s.length();i++){
            if(s.charAt(i)=='1'){
                count++;
            }
        }
        if(count==0){
            return (int)(((n-1)*(n-2)/2)%d);//this formula can't understand 
        }
        if(count%3!=0) return 0;
        long gap1=0,gap2=0,countone=0;
        for(int i=0;i<s.length();i++){
            if(s.charAt(i)=='1'){
                countone++;
            }
            if(countone==count/3){
                while(i<s.length()-1&&s.charAt(i+1)=='0'){
                    gap1++;
                    i++;
                }
            }
             if(countone==2*count/3){
                while(i<s.length()-1&&s.charAt(i+1)=='0'){
                    gap2++;
                    i++;
                }
            }
            
        }
       //1001|0|0|0|11|0|0|101 after 2 one we have a gap 0f 3 zeros so we can make 4 cuts like 1001,10010,100100,1001000 these all re having only 2 ones gap so possible combination are gap+1 where gap is no of 0's after total no of ones/3 ie first string of 1's.
        return (int)((gap1+1)*(gap2+1)%d);
    }
}