LeetCode Entry

2996. Smallest Missing Integer Greater Than Sequential Prefix Sum

11.08.2026 easy 2026 kotlin rust

First prefix sum not in the array

2996. Smallest Missing Integer Greater Than Sequential Prefix Sum easy substack youtube

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Problem TLDR

First prefix sum not in the array

Intuition

• brute force, only 50 elements
• max is 50, max prefix sum 50^2
• check only the current position: n[i] == n[0] + i
• use bitmask instead of a set
• don’t check sum if it is bigger than max

Approach

• kotlin: (sum…) - n.toSet() then take first
• rust: (n[0]..) gives the expected sequence

Complexity

• Time complexity: \(O(n^2)\)

• Space complexity: \(O(1)\)

Code

    fun missingInteger(n: IntArray) =
    ((n.indices.takeWhile{n[it]==n[0]+it}.sumOf{n[it]}..2500)-n.toSet())[0]

    pub fn missing_integer(n: Vec<i32>) -> i32 {
        (n.iter().zip(n[0]..).take_while(|(a, b)| *a == b).map(|x| x.1).sum()..)
        .find(|x| !n.contains(x)).unwrap()
    }