Solution.cpp

class Solution {
public:
    bool circularArrayLoop(vector<int>& nums) {
        int n = nums.size();
        for (int i = 0; i < n; ++i) {
            if (!nums[i]) continue;
            int slow = i, fast = next(nums, i);
            while (nums[slow] * nums[fast] > 0 && nums[slow] * nums[next(nums, fast)] > 0) {
                if (slow == fast) {
                    if (slow != next(nums, slow)) return true;
                    break;
                }
                slow = next(nums, slow);
                fast = next(nums, next(nums, fast));
            }
            int j = i;
            while (nums[j] * nums[next(nums, j)] > 0) {
                nums[j] = 0;
                j = next(nums, j);
            }
        }
        return false;
    }

    int next(vector<int>& nums, int i) {
        int n = nums.size();
        return (i + nums[i] % n + n) % n;
    }
};