[LeetCode] 2270. Number of Ways to Split Array (Python)

 

난이도: Medium

 

문제 설명

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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.

 

문제 예제

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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.

 

제한 사항

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• 2 <= nums.length <= 10^5
• -105 <= nums[i] <= 10^5

 

✏️ Solution(솔루션)

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class Solution:
    def waysToSplitArray(self, nums: List[int]) -> int:
        n = len(nums)
        answer = 0
        prefix = [0 for _ in range(n)]
        suffix = [0 for _ in range(n)]

        prefix[0] = nums[0]
        suffix[-1] = nums[-1]

        for i in range(1, n):
            prefix[i] = prefix[i-1] + nums[i]
        
        for i in range(n-2, -1, -1):
            suffix[i] = suffix[i+1] + nums[i]

        for i in range(n-1):
            if prefix[i] >= suffix[i+1]:
                answer += 1
        
        return answer

 

먼저 prefix와 suffix 라는 리스트를 만들었다.

 

prefix는 누적합을 저장하는 리스트이다.

ex) Input: [10, 4, -8, 7] ==> prefix = [10, 14, 6, 13]

 

suffix는 배열의 끝에서부터 누적합을 저장하는 리스트이다.

ex) Input: [10, 4, -8, 7] ==> suffix = [13 ,3,-1, 7]

 

prefix와 suffix 리스트가 모두 저장 완료되면 n-1번 도는 for문을 선언했다.

각 반복마다 prefix[i]와 suffix[i+1]을 비교하여 조건을 만족하면 answer를 +1 해주었다.

 

마지막으로 answer를 return하여 정답을 맞출 수 있었다.

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문제: 2270. Number of Ways to Split Array

깃허브: github

algorithm_practice/LeetCode/2358-number-of-ways-to-split-array at main · laewonJeong/algorithm_practice