## 565. Array Nesting

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: 4
Explanation:
A = 5, A = 4, A = 0, A = 3, A = 1, A = 6, A = 2.

One of the longest S[K]:
S = {A, A, A, A} = {5, 6, 2, 0}
```

Note:

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

## Rust Solution

``````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);
}
``````

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