{ "data": { "question": { "questionId": "457", "questionFrontendId": "457", "categoryTitle": "Algorithms", "boundTopicId": 1415, "title": "Circular Array Loop", "titleSlug": "circular-array-loop", "content": "
You are playing a game involving a circular array of non-zero integers nums
. Each nums[i]
denotes the number of indices forward/backward you must move if you are located at index i
:
nums[i]
is positive, move nums[i]
steps forward, andnums[i]
is negative, move nums[i]
steps backward.Since the array is circular, you may assume that moving forward from the last element puts you on the first element, and moving backwards from the first element puts you on the last element.
\n\nA cycle in the array consists of a sequence of indices seq
of length k
where:
seq[0] -> seq[1] -> ... -> seq[k - 1] -> seq[0] -> ...
nums[seq[j]]
is either all positive or all negative.k > 1
Return true
if there is a cycle in nums
, or false
otherwise.
\n
Example 1:
\n\nInput: nums = [2,-1,1,2,2]\nOutput: true\nExplanation: The graph shows how the indices are connected. White nodes are jumping forward, while red is jumping backward.\nWe can see the cycle 0 --> 2 --> 3 --> 0 --> ..., and all of its nodes are white (jumping in the same direction).\n\n\n
Example 2:
\n\nInput: nums = [-1,-2,-3,-4,-5,6]\nOutput: false\nExplanation: The graph shows how the indices are connected. White nodes are jumping forward, while red is jumping backward.\nThe only cycle is of size 1, so we return false.\n\n\n
Example 3:
\n\nInput: nums = [1,-1,5,1,4]\nOutput: true\nExplanation: The graph shows how the indices are connected. White nodes are jumping forward, while red is jumping backward.\nWe can see the cycle 0 --> 1 --> 0 --> ..., and while it is of size > 1, it has a node jumping forward and a node jumping backward, so it is not a cycle.\nWe can see the cycle 3 --> 4 --> 3 --> ..., and all of its nodes are white (jumping in the same direction).\n\n\n
\n
Constraints:
\n\n1 <= nums.length <= 5000
-1000 <= nums[i] <= 1000
nums[i] != 0
\n
Follow up: Could you solve it in O(n)
time complexity and O(1)
extra space complexity?
存在一个不含 0
的 环形 数组 nums
,每个 nums[i]
都表示位于下标 i
的角色应该向前或向后移动的下标个数:
nums[i]
是正数,向前(下标递增方向)移动 |nums[i]|
步nums[i]
是负数,向后(下标递减方向)移动 |nums[i]|
步因为数组是 环形 的,所以可以假设从最后一个元素向前移动一步会到达第一个元素,而第一个元素向后移动一步会到达最后一个元素。
\n\n数组中的 循环 由长度为 k
的下标序列 seq
标识:
seq[0] -> seq[1] -> ... -> seq[k - 1] -> seq[0] -> ...
nums[seq[j]]
应当不是 全正 就是 全负k > 1
如果 nums
中存在循环,返回 true
;否则,返回 false
。
\n\n
示例 1:
\n\n输入:nums = [2,-1,1,2,2]\n输出:true\n解释:图片展示了节点间如何连接。白色节点向前跳跃,而红色节点向后跳跃。\n我们可以看到存在循环,按下标 0 -> 2 -> 3 -> 0 --> ...,并且其中的所有节点都是白色(以相同方向跳跃)。\n\n\n
示例 2:
\n\n输入:nums = [-1,-2,-3,-4,-5,6]\n输出:false\n解释:图片展示了节点间如何连接。白色节点向前跳跃,而红色节点向后跳跃。\n唯一的循环长度为 1,所以返回 false。\n\n\n
示例 3:
\n\n输入:nums = [1,-1,5,1,4]\n输出:true\n解释:图片展示了节点间如何连接。白色节点向前跳跃,而红色节点向后跳跃。\n我们可以看到存在循环,按下标 0 --> 1 --> 0 --> ...,当它的大小大于 1 时,它有一个向前跳的节点和一个向后跳的节点,所以 它不是一个循环。\n我们可以看到存在循环,按下标 3 --> 4 --> 3 --> ...,并且其中的所有节点都是白色(以相同方向跳跃)。\n\n\n
\n\n
提示:
\n\n1 <= nums.length <= 5000
-1000 <= nums[i] <= 1000
nums[i] != 0
\n\n
进阶:你能设计一个时间复杂度为 O(n)
且额外空间复杂度为 O(1)
的算法吗?
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