565. Array Nesting

Posted 2020-10-05 无惧风云

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].

    1 class Solution {
    2 public:
    3     int arrayNesting(vector<int>& nums) {
    4             int len = nums.size();
    5         int N = len;
    6         int max = 0;
    7         int result = 0;
    8         for (int i = 0;i < len;i++)
    9         {
   10             if (nums[i] == N)
   11             {
   12                 continue;
   13             }
   14             else
   15             {
   16                 int k = i;
   17                 while (k < len&&nums[k] != N)
   18                 {
   19                     max++;
   20                     int k1 =nums[k];
   21                     nums[k] = N;
   22                     k = k1;
   23                 }
   24             }
   25             if (max > result)
   26             {
   27                 result = max;
   28             
   29             }
   30                 max = 0;
   31         }
   32         return result;
   33     }
   34 };