[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:

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].

思路：要求s[k]最多的元素个数， 利用一个boolean[]数组，判断每次循环s[k]的长度

package com.billkang;/** * @author binkang * @date May 28, 2017 */public class ArrayNesting {public int arrayNesting(int[] nums) {int len = nums.length;if(len == 1) {return 1;}boolean[] mark = new boolean[len];//init mark//for(int i=0;i<len;i++) {//mark[i] = false;//}int longest = 0;for(int i=0;i<len;i++) {int k=i;int count = 0;while(!mark[k]) {count++;mark[i] = !mark[k];k = nums[k];}longest = Math.max(longest, count);}return longest;}}