## 题目描述：

LeetCode 565. Array Nesting

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.

Example 1:

```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}
```

Note:

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

## 题目大意：

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

1. N是整数，范围[1, 20000]
2. A中的元素各不相同
3. A是整数，范围[0, N - 1]

DFS / 并查集

## Python代码：

``````class Solution(object):
def arrayNesting(self, nums):
"""
:type nums: List[int]
:rtype: int
"""
def search(idx):
cnt = 0
while nums[idx] >= 0:
cnt += 1
next = nums[idx]
nums[idx] = -1
idx = next
return cnt
ans = 0
for x in range(len(nums)):
if nums[x] >= 0:
ans = max(ans, search(x))
return ans
``````

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