Package g0401_0500.s0457_circular_array_loop

Class Solution

java.lang.Object
g0401_0500.s0457_circular_array_loop.Solution
public class Solution extends java.lang.Object
457 - Circular Array Loop.

Medium

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:

  • If nums[i] is positive, move nums[i] steps forward , and
  • If nums[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.

A cycle in the array consists of a sequence of indices seq of length k where:

  • Following the movement rules above results in the repeating index sequence seq[0] -> seq[1] -> ... -> seq[k - 1] -> seq[0] -> ...
  • Every nums[seq[j]] is either all positive or all negative.
  • k > 1

Return true if there is a cycle in nums, or false otherwise.

Example 1:

Input: nums = [2,-1,1,2,2]

Output: true

Explanation: There is a cycle from index 0 -> 2 -> 3 -> 0 -> … The cycle’s length is 3.

Example 2:

Input: nums = [-1,2]

Output: false

Explanation: The sequence from index 1 -> 1 -> 1 -> … is not a cycle because the sequence’s length is 1. By definition the sequence’s length must be strictly greater than 1 to be a cycle.

Example 3:

Input: nums = [-2,1,-1,-2,-2]

Output: false

Explanation: The sequence from index 1 -> 2 -> 1 -> … is not a cycle because nums[1] is positive, but nums[2] is negative. Every nums[seq[j]] must be either all positive or all negative.

Constraints:

  • 1 <= nums.length <= 5000
  • -1000 <= nums[i] <= 1000
  • nums[i] != 0

Follow up: Could you solve it in O(n) time complexity and O(1) extra space complexity?

  • Constructor Summary

    Constructors
    Constructor
    Description
    Solution()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    boolean
    circularArrayLoop(int[] arr)
     

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • Solution

      public Solution()

  • Method Details

    • circularArrayLoop

      public boolean circularArrayLoop(int[] arr)