# 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[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 A is an integer within the range [0, N-1].

class Solution {
public:
int arrayNesting(vector<int>& nums) {
int n = nums.size(), res = INT_MIN;
vector<bool> visited(n, false);
for (int i = 0; i < nums.size(); ++i) {
if (visited[nums[i]]) continue;
res = max(res, helper(nums, i, visited));
}
return res;
}
int helper(vector<int>& nums, int start, vector<bool>& visited) {
int i = start, cnt = 0;
while (cnt == 0 || i != start) {
visited[i] = true;
i = nums[i];
++cnt;
}
return cnt;
}
};

class Solution {
public:
int arrayNesting(vector<int>& nums) {
int n = nums.size(), res = INT_MIN;
vector<bool> visited(n, false);
for (int i = 0; i < n; ++i) {
if (visited[nums[i]]) continue;
int cnt = 0, j = i;
while(cnt == 0 || j != i) {
visited[j] = true;
j = nums[j];
++cnt;
}
res = max(res, cnt);
}
return res;
}
};

class Solution {
public:
int arrayNesting(vector<int>& nums) {
int n = nums.size(), res = 0;
for (int i = 0; i < n; ++i) {
int cnt = 1;
while (nums[i] != i) {
swap(nums[i], nums[nums[i]]);
++cnt;
}
res = max(res, cnt);
}
return res;
}
};

Github 同步地址：

https://github.com/grandyang/leetcode/issues/565

Nested List Weight Sum II

Nested List Weight Sum

https://leetcode.com/problems/array-nesting/

https://leetcode.com/problems/array-nesting/discuss/102432/C%2B%2B-Java-Clean-Code-O(N)

https://leetcode.com/problems/array-nesting/discuss/232283/C%2B%2B-straightforward-solution-beats-100

LeetCode All in One 题目讲解汇总(持续更新中…)

 微信打赏 Venmo 打赏
（欢迎加入博主的知识星球，博主将及时答疑解惑，并分享刷题经验与总结，试运营期间前五十位可享受半价优惠～）

×

Help us with donation