(判环)457. 环形数组是否存在循环

457. 环形数组是否存在循环

class Solution {
 public:
  bool circularArrayLoop(vector<int>& nums) {
    int n = nums.size();
    auto next = [&](int x) { return ((x + nums[x]) % n + n) % n; };

    for (int i = 0; i < n; i++) {
      int slow = i, fast = next(i);
      if (!nums[slow]) continue;
      if (nums[slow] * nums[fast] <= 0) continue;
      while (nums[fast] * nums[next(fast)] > 0) {
        if (!nums[slow]) break;
        if (slow == fast) {
          if (slow != next(slow))
            return true;
          else
            break;
        }
        slow = next(slow);
        fast = next(next(fast));
      }
      int add = i;
      while (nums[add] * nums[next(add)] > 0) {
        int t = add;
        add = next(add);
        nums[t] = 0;
      }
    }
    return false;
  }
};