LeetCode Entry

2598. Smallest Missing Non-negative Integer After Operations

16.10.2025 medium 2025 kotlin rust

First positive number can't be build by adding/subtracting value

2598. Smallest Missing Non-negative Integer After Operations medium blog post substack youtube

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Problem TLDR

First positive number can’t be build by adding/subtracting value #medium #hashmap

Intuition

Iterate from zero and look for the reminder. Use it or stop.

Approach

• corner case: negatives
• we can use array size of v as a frequency map

Complexity

• Time complexity: \(O(n)\)

• Space complexity: \(O(n)\)

Code

// 135ms
    fun findSmallestInteger(n: IntArray, v: Int): Int {
        val m = n.groupBy{ (it%v+v)%v }.mapValues{ it.value.size }.toMutableMap()
        return (0..n.size).first { val c = m[it%v]?:0; m[it%v]=c-1; c < 1 }
    }

// 0ms
    pub fn find_smallest_integer(n: Vec<i32>, v: i32) -> i32 {
        let mut f = vec![0; v as usize]; for &x in &n { f[((x%v+v)%v) as usize] += 1 }
        (0..=n.len()).find(|x| { let c = f[x%v as usize]; f[x%v as usize] -= 1; c < 1 }).unwrap() as _
    }