Solution.java

class Solution {
    private int n;
    private int[] nums;

    public boolean circularArrayLoop(int[] nums) {
        n = nums.length;
        this.nums = nums;
        for (int i = 0; i < n; ++i) {
            if (nums[i] == 0) {
                continue;
            }
            int slow = i, fast = next(i);
            while (nums[slow] * nums[fast] > 0 && nums[slow] * nums[next(fast)] > 0) {
                if (slow == fast) {
                    if (slow != next(slow)) {
                        return true;
                    }
                    break;
                }
                slow = next(slow);
                fast = next(next(fast));
            }
            int j = i;
            while (nums[j] * nums[next(j)] > 0) {
                nums[j] = 0;
                j = next(j);
            }
        }
        return false;
    }

    private int next(int i) {
        return (i + nums[i] % n + n) % n;
    }
}