[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: 4Explanation: 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 array A is an integer within the range [0, N-1].

class Solution {public:    int arrayNesting(vector<int>& nums) {        int MaxLen = 1;        for (int i = 0; i < nums.size(); i++) {            if (nums[i] <= 0) continue;            int start = i, ptr = i, Len = 0;            while (nums[ptr] != start) {                nums[ptr] = -nums[ptr];                ptr = -nums[ptr];                Len++;            }            nums[ptr] = -nums[ptr];            MaxLen = max(MaxLen, Len + 1);        }        return MaxLen;    }};

// clearer codeclass Solution {public:    int arrayNesting(vector<int>& nums) {        int MaxLen = 1;        for (int i = 0; i < nums.size(); i++) {            int Len = 0;            for (int ptr = i; nums[ptr] >= 0; Len++) {                int tmp = nums[ptr];                nums[ptr] = -1;                ptr = tmp;            }            MaxLen = max(MaxLen, Len);        }        return MaxLen;    }};