Floyd's algorithm will eventually find any cycle that exists, even if we start from index 0

class Solution {

  public boolean loopExists(int[] arr) {
    int slow = 0;
    int fast = 0;
    do{
      slow = getNext(arr, slow);
      fast = getNext(arr, getNext(arr, fast));
    }while(slow!=fast);

    int length =  getCycleLength(arr,slow) ;
    return length>1;
  }

  int getNext(int a[], int index){
    int val = a[index]+a.length+index;
    return val%a.length;
  }

  int getCycleLength(int a[], int slow){
    int index = slow;
    boolean isNegative = false;
    boolean isPositive = false;
    int count = 0;
    if(a[slow]>0){
      isPositive = true;
    }else{
      isNegative = true;
    }
    do{
      index = getNext(a, index);
      if(a[index]>0){
        isPositive = true;
      }else{
        isNegative = true;
      }
      count++;
    }while(index!=slow);

    if(isNegative && isPositive){
      return 0;
    }
    return count ;
  }

}