A zero-indexed array A of length N contains all integers from 0 to N-1. Find and return the longest length of set S, where S[i] = {A[i], A[A[i]], A[A[A[i]]], ... } subjected to the rule below.

Suppose the first element in S starts with the selection of element A[i] of index = i, the next element in S should be A[A[i]], and then A[A[A[i]]]… By that analogy, we stop adding right before a duplicate element occurs in S.

**Example 1:**

Input:A = [5,4,0,3,1,6,2]Output:4Explanation: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}

**Note:**

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

```
struct Solution;
impl Solution {
fn array_nesting(nums: Vec<i32>) -> i32 {
let mut res = 0;
let n = nums.len();
let mut visited = vec![false; n];
for i in 0..n {
if visited[i] {
continue;
}
let mut j = i;
let mut length = 0;
while !visited[j] {
visited[j] = true;
j = nums[j] as usize;
length += 1;
}
res = res.max(length);
}
res
}
}
#[test]
fn test() {
let nums = vec![5, 4, 0, 3, 1, 6, 2];
let res = 4;
assert_eq!(Solution::array_nesting(nums), res);
}
```