動機
0~n就是loop!!
Problem
You are given an integer array nums
of length n
where nums
is a permutation of the numbers in the range [0, n - 1]
.
You should build a set s[k] = {nums[k], nums[nums[k]], nums[nums[nums[k]]], ... }
subjected to the following rule:
- The first element in
s[k]
starts with the selection of the elementnums[k]
ofindex = k
. - The next element in
s[k]
should benums[nums[k]]
, and thennums[nums[nums[k]]]
, and so on. - We stop adding right before a duplicate element occurs in
s[k]
.
Return the longest length of a set s[k]
.
Example 1:
Input: nums = [5,4,0,3,1,6,2]Output: 4Explanation: nums[0] = 5, nums[1] = 4, nums[2] = 0, nums[3] = 3, nums[4] = 1, nums[5] = 6, nums[6] = 2.One of the longest sets s[k]:s[0] = {nums[0], nums[5], nums[6], nums[2]} = {5, 6, 2, 0}
Example 2:
Input: nums = [0,1,2]Output: 1
Constraints:
1 <= nums.length <= 105
0 <= nums[i] < nums.length
- All the values of
nums
are unique.
Sol
只要是排序就是會有各種loop,所以用dfs去求loop長度就好
class Solution:
def arrayNesting(self, nums: List[int]) -> int:
def dfs(i):
if i == -1:
return -1
else:
j, nums[i] = nums[i], -1
return 1+dfs(j)
return max([dfs(i) for i in range(len(nums))])