Leetcode 457 Solution

class Solution {
    vector<int>* pnums;
public:
    int next(int i)
    {
        return (i + (*pnums)[i] + (*pnums).size()) % (*pnums).size();
    }

    bool circularArrayLoop(vector<int>& nums) {
        if (nums.size() == 0)
            return false;

        pnums = &nums;

        for (int i = 0; i < nums.size(); i++)
        {
            if (nums[i] == 0)
                continue;

            int slow = i;
            int fast = i;

            while (nums[fast] * nums[next(fast)] > 0 && nums[next(fast)] * nums[next(next(fast))] > 0)
            {
                slow = next(slow);
                fast = next(next(fast));

                if (slow == fast)
                {
                    if (slow == next(slow))
                        break;

                    printf("%d\n", slow);
                    return true;
                }
            }

            slow = i;
            while (nums[i] * nums[next(i)] > 0)
            {
                nums[i] = 0;
                i = next(i);
            }
        }

        return false;
    }
};