``````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[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].``````

``````class Solution {
public:
int arrayNesting(vector<int>& nums) {
int n = nums.size();
int res = 0;
for(int i = 0;i < n;i++)
{
int start = nums[i],count = 0;
do
{
start = nums[start];
count++;
}while(start != nums[i]);

res = max(res,count);
}

return res;
}
};``````

``````856 / 856 test cases passed, but took too long.
Status: Time Limit Exceeded
Submitted: 6 minutes ago``````

``````class Solution {
public:
int arrayNesting(vector<int>& nums) {
int n = nums.size();
vector<bool> visited(n,false);
int res = 0;
for(int i = 0;i < n;i++)
{
if(!visited[i])
{
int start = nums[i],count = 0;
do
{
start = nums[start];
count++;
visited[start] = true;
}while(start != nums[i]);

res = max(res,count);
}
}

return res;
}
};``````

``````Runtime: 36 ms, faster than 77.76% of C++ online submissions for Array Nesting.
Memory Usage: 30.3 MB, less than 40.35% of C++ online submissions for Array Nesting.``````

``````class Solution {
public:
int arrayNesting(vector<int>& nums) {
int n = nums.size();
int res = 0;
for(int i = 0;i < n;i++)
{
if(INT_MIN != nums[i])
{
int start = nums[i],count = 0;
//这里需要格外注意，因为我们改变了vector的值，需要将原来的判断逻辑修改为判断是否等于INT_MIN
while(INT_MIN != nums[start])
{
int temp = start;
start = nums[start];
count++;
nums[temp] = INT_MIN;
}
res = max(count,res);
}
}

return res;
}
};``````

``````Runtime: 24 ms, faster than 99.65% of C++ online submissions for Array Nesting.
Memory Usage: 30.2 MB, less than 56.82% of C++ online submissions for Array Nesting.``````