力扣：565. 数组嵌套

import java.util.ArrayList;
import java.util.List;


public class Solution {
    public static void main(String[] args) {
        Solution solution = new Solution();
        int[] A = {5,4,0,3,1,6,2};
        System.out.println(solution.arrayNesting3(A));
    }

    
    public int arrayNesting(int[] nums) {
        int ans = 0;
        for (int i = 0; i < nums.length; i++){
            ans = Math.max(calculation(nums, i), ans);
        }
        return ans;
    }

    private int calculation(int[] nums, int begin){
        List list = new ArrayList<>();
        while (!list.contains(begin)){
            list.add(begin);
            begin = nums[begin];
        }
        return list.size();
    }

    
    public int arrayNesting2(int[] nums) {
        int res = 0;
        boolean[] visited = new boolean[nums.length];
        for (int i = 0; i < nums.length; i++){
            if (!visited[i]){
                // 记录一下环口，如果到了环口退出
                int begin = nums[i], count = 1;
                while (begin != i) {
                    begin = nums[begin];
                    count++;
                    visited[begin] = true;
                }
                res = Math.max(res, count);
            }
        }
        return res;
    }

    
    public int arrayNesting3(int[] nums) {
        int res = 0;
        for (int i = 0; i < nums.length; i++){
            if (nums[i] != -1){
                int start = nums[i], count = 1;
                while (start != -1){
                    // 提前存储结果
                    int temp = start;
                    start = nums[start];
                    count++;
                    nums[temp] = -1;
                }
                res = Math.max(res, count);
            }
        }
        return res;
    }
}