1. Description

A zero-indexed array A consisting of N different integers is given. The array contains all integers in the range [0, N - 1].

Sets S[K] for 0 <= K < N are defined as follows:

S[K] = { A[K], A[A[K]], A[A[A[K]]], ... }.

Sets S[K] are finite for each K and should NOT contain duplicates.

Write a function that given an array A consisting of N integers, return the size of the largest set S[K] for this array.

Note:

N is an integer within the range [1, 20,000].
The elements of A are all distinct.
Each element of array A is an integer within the range [0, N-1].

2. Runtime Distribution

3. Submission Details

4. Example

Input: A = [5,4,0,3,1,6,2]
Output: 4
Explanation:
A[0] = 5, A[1] = 4, A[2] = 0, A[3] = 3, A[4] = 1, A[5] = 6, A[6] = 2.
One of the longest S[K]:
S[0] = {A[0], A[5], A[6], A[2]} = {5, 6, 2, 0}

5. Code

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public int arrayNesting(int[] nums) {
	if (nums == null || nums.length == 0) {
		return 0;
	}

	int result = 0;
	int half = nums.length >> 1;
	for (int i = 0; i < nums.length; i++) {
		int count = 0;
		for (int j = i; nums[j] != -1; count++) {
			int tmp = nums[j];
			nums[j] = -1;
			j = tmp;
		}
		if (count > half) {
			return count;
		}
		result = Math.max(result, count);
	}
	return result;
}

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6.Test

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public class LeetCode0565 {
	public int arrayNesting(int[] nums) {
		if (nums == null || nums.length == 0) {
			return 0;
		}

		int result = 0;
		int half = nums.length >> 1;
		for (int i = 0; i < nums.length; i++) {
			int count = 0;
			for (int j = i; nums[j] != -1; count++) {
				int tmp = nums[j];
				nums[j] = -1;
				j = tmp;
			}
			if (count > half) {
				return count;
			}
			result = Math.max(result, count);
		}
		return result;
	}

	public static void main(String[] args) {
		LeetCode0565 leetcode = new LeetCode0565();
		int[] nums = new int[] { 5, 4, 0, 3, 1, 6, 2 };
		System.out.println(leetcode.arrayNesting(nums));
	}
}

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