Leetcode 3432. Count Partitions with Even Sum Difference

Problem

You are given an integer array nums of length n.

A partition is defined as an index i where 0 <= i < n - 1, splitting the array into two non-empty subarrays such that:

• Left subarray contains indices 0, i.
• Right subarray contains indices i + 1, n - 1.

Return the number of partitions where the difference between the sum of the left and right subarrays is even.

Algorithm

Translate into English: Given an array, compute all possible partitioning methods such that the difference between the sum of the left subarray and the sum of the right subarray is even. A partitioning method refers to dividing the array into non-empty left and right subarrays.

Code

class Solution:
    def countPartitions(self, nums: List[int]) -> int:
        sum_n, len_n = sum(nums), len(nums)
        l_v, r_v, cnts = 0, sum_n, 0
        for i in range(len_n-1):
            l_v += nums[i]
            r_v -=nums[i]
            if (l_v - r_v) % 2 == 0:
                cnts += 1
        return cnts