题目：

题解：

func circularArrayLoop(nums []int) bool {
    n := len(nums)
    next := func(cur int) int {
        return ((cur+nums[cur])%n + n) % n // 保证返回值在 [0,n) 中
    }

    for i, num := range nums {
        if num == 0 {
            continue
        }
        slow, fast := i, next(i)
        // 判断非零且方向相同
        for nums[slow]*nums[fast] > 0 && nums[slow]*nums[next(fast)] > 0 {
            if slow == fast {
                if slow == next(slow) {
                    break
                }
                return true
            }
            slow = next(slow)
            fast = next(next(fast))
        }
        add := i
        for nums[add]*nums[next(add)] > 0 {
            tmp := add
            add = next(add)
            nums[tmp] = 0
        }
    }
    return false
}