class Solution {
public:
    bool isCircle(int start, vector<int> &nums, vector<int> &flags) {
        set<int> paths;
        paths.insert(start);

        int idx = start;
        int nextIdx = start + nums[start];
        while (nextIdx < 0)
            nextIdx += nums.size();


        while (nums[idx] * nums[nextIdx % nums.size()] > 0
        && idx != nextIdx % nums.size()
        && flags[nextIdx % nums.size()] != -1) {
            if (paths.find(nextIdx % nums.size()) != paths.end()) {
                return true;
            }


            idx = nextIdx % nums.size();
            nextIdx = idx + nums[idx];

            while (nextIdx < 0)
                nextIdx += nums.size();

            paths.insert(idx);

        } 


        for (auto &x : paths)
            flags[x] = -1;

        return false;
    }

    bool circularArrayLoop(vector<int>& nums) {
        vector<int> flags(nums.size(), 0);

        for (int i = 0; i < nums.size(); i++) {
            if (isCircle(i, nums, flags))
                return true;
            else
                flags[i] = -1;
        }

        return false;
    }
};