Leetcode题解

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:
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].

本质来说此题就是一个DFS，我的方法是用一个数组记录每个元素的访问次数，从每个元素出发做DFS找到最大的计数，然后每个元素相比较，找到所有情况中的最大计数，返回即可。

链接

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