2270. Number of Ways to Split Array

Problem

You are given a 0-indexed integer array nums of length n.

nums contains a valid split at index i if the following are true:

• The sum of the first i + 1 elements is greater than or equal to the sum of the last n - i - 1 elements.
• There is at least one element to the right of i. That is, 0 <= i < n - 1.

Return the number of valid splits in nums.

https://leetcode.com/problems/number-of-ways-to-split-array/

Example 1:

Input: nums = [10,4,-8,7]
Output: 2
Explanation:
There are three ways of splitting nums into two non-empty parts:

• Split nums at index 0. Then, the first part is [10], and its sum is 10. The second part is [4,-8,7], and its sum is 3. Since 10 >= 3, i = 0 is a valid split.
• Split nums at index 1. Then, the first part is [10,4], and its sum is 14. The second part is [-8,7], and its sum is -1. Since 14 >= -1, i = 1 is a valid split.
• Split nums at index 2. Then, the first part is [10,4,-8], and its sum is 6. The second part is [7], and its sum is 7. Since 6 < 7, i = 2 is not a valid split.

Thus, the number of valid splits in nums is 2.

Example 2:

Input: nums = [2,3,1,0]
Output: 2
Explanation:
There are two valid splits in nums:

• Split nums at index 1. Then, the first part is [2,3], and its sum is 5. The second part is [1,0], and its sum is 1. Since 5 >= 1, i = 1 is a valid split.
• Split nums at index 2. Then, the first part is [2,3,1], and its sum is 6. The second part is [0], and its sum is 0. Since 6 >= 0, i = 2 is a valid split.

Constraints:

• 2 <= nums.length <= 10⁵
• -10⁵ <= nums[i] <= 10⁵

Test Cases

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Tclass Solution:
    def waysToSplitArray(self, nums: List[int]) -> int:

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import pytest

from solution import Solution


@pytest.mark.parametrize('nums, expected', [
    ([10,4,-8,7], 2),
    ([2,3,1,0], 2),
])
@pytest.mark.parametrize('sol', [Solution()])
def test_solution(sol, nums, expected):
    assert sol.waysToSplitArray(nums) == expected

Thoughts

先计算出整个 nums 的总和。

从 i = 0 开始遍历，累加左半数组的和，根据总和可以算出右半数组之和，比较即可。

Code

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class Solution:
    def waysToSplitArray(self, nums: list[int]) -> int:
        total = sum(nums)
        valid = 0
        left = 0
        for i in range(len(nums) - 1):
            left += nums[i]
            if left >= total - left: valid += 1

        return valid

许可协议

本文除了题目描述（Problem）部分之外，其他内容由 Calf 原创，采用 CC BY-NC-SA 4.0 许可协议，转载请注明出处。

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