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3236. Smallest Missing Integer Greater Than Sequential Prefix Sum

My accepted Python solution to LeetCode problem 3236, Smallest Missing Integer Greater Than Sequential Prefix Sum, running in 3ms.

  • Difficulty: Easy
  • Python
  • Runtime 3ms
  • Memory 17.2MB

Read the problem on LeetCode View on GitHub

The problem statement is LeetCode’s and stays on their site. What follows is my accepted solution.

Python

Accepted on LeetCode — runtime 3ms, memory 17.2MB, accepted 2026-01-02.

python
class Solution:
    def missingInteger(self, nums: List[int]) -> int:
        # Find longest sequential prefix
        prefix_sum = nums[0]
        for i in range(1, len(nums)):
            if nums[i] == nums[i-1] + 1:
                prefix_sum += nums[i]
            else:
                break
        
        # Find smallest missing integer >= prefix_sum
        nums_set = set(nums)
        result = prefix_sum
        while result in nums_set:
            result += 1
        return result

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