[LeetCode] 2348. Number of Zero-Filled Subarrays (Medium/Python)

Number of Zero-Filled Subarrays - LeetCode

Above is the link to the problem.

 

Problem

Given an integer array nums, return the number of "subarrays" filled with 0.

A "subarray" is a contiguous non-empty sequence of elements within an array.

 

Example 1:

Input: nums = [1,3,0,0,2,0,0,4]

Output: 6

Explanation:

There are 4 occurrences of [0] as a subarray.

There are 2 occurrences of [0,0] as a subarray.

There is no occurrence of a subarray with a size more than 2 filled with 0. 

Therefore, we return 6.

 

Example 2:

Input: nums = [0,0,0,2,0,0]

Output: 9

Explanation:

There are 5 occurrences of [0] as a subarray.

There are 3 occurrences of [0,0] as a subarray.

There is 1 occurrence of [0,0,0] as a subarray.

There is no occurrence of a subarray with a size more than 3 filled with 0. 

Therefore, we return 9.

 

Example 3:

Input: nums = [2,10,2019]

Output: 0

Explanation: 

There is no subarray filled with 0. 

Therefore, we return 0.

 

Analysis

If there exist consecutive 0

like 0, 0, 0 

there are 3 possible ways [0, 0, 0]  and [0, 0] and [0]

and each way has 1([0, 0, 0]) + 2([0, 0]) + 3([0]) cases.

 

Code

This code has O(n) time complexity.