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565. Array Nesting

Description

You are given an integer array nums of length n where nums is a permutation of the numbers in the range [0, n - 1].

You should build a set s[k] = {nums[k], nums[nums[k]], nums[nums[nums[k]]], ... } subjected to the following rule:

• The first element in s[k] starts with the selection of the element nums[k] of index = k.
• The next element in s[k] should be nums[nums[k]], and then nums[nums[nums[k]]], and so on.
• We stop adding right before a duplicate element occurs in s[k].

Return the longest length of a set s[k].

 

Example 1:

Input: nums = [5,4,0,3,1,6,2]
Output: 4
Explanation: 
nums[0] = 5, nums[1] = 4, nums[2] = 0, nums[3] = 3, nums[4] = 1, nums[5] = 6, nums[6] = 2.
One of the longest sets s[k]:
s[0] = {nums[0], nums[5], nums[6], nums[2]} = {5, 6, 2, 0}

Example 2:

Input: nums = [0,1,2]
Output: 1

 

Constraints:

• 1 <= nums.length <= 105
• 0 <= nums[i] < nums.length
• All the values of nums are unique.

Solutions

• Java
• C++
• Python
• Go

• class Solution {
      public int arrayNesting(int[] nums) {
          int ans = 0, n = nums.length;
          for (int i = 0; i < n; ++i) {
              int cnt = 0;
              int j = i;
              while (nums[j] < n) {
                  int k = nums[j];
                  nums[j] = n;
                  j = k;
                  ++cnt;
              }
              ans = Math.max(ans, cnt);
          }
          return ans;
      }
  }
  
  

• class Solution {
  public:
      int arrayNesting(vector<int>& nums) {
          int ans = 0, n = nums.size();
          for (int i = 0; i < n; ++i) {
              int cnt = 0;
              int j = i;
              while (nums[j] < n) {
                  int k = nums[j];
                  nums[j] = n;
                  j = k;
                  ++cnt;
              }
              ans = max(ans, cnt);
          }
          return ans;
      }
  };
  

• class Solution:
      def arrayNesting(self, nums: List[int]) -> int:
          ans, n = 0, len(nums)
          for i in range(n):
              cnt = 0
              while nums[i] != n:
                  j = nums[i]
                  nums[i] = n
                  i = j
                  cnt += 1
              ans = max(ans, cnt)
          return ans
  
  

• func arrayNesting(nums []int) int {
  	ans, n := 0, len(nums)
  	for i := range nums {
  		cnt, j := 0, i
  		for nums[j] != n {
  			k := nums[j]
  			nums[j] = n
  			j = k
  			cnt++
  		}
  		if ans < cnt {
  			ans = cnt
  		}
  	}
  	return ans
  }
  

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