LeetCode Entry

3751. Total Waviness of Numbers in Range I

04.06.2026 medium 2026 kotlin rust

Count hills and valleys base10 in a..b

3751. Total Waviness of Numbers in Range I medium substack youtube

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Problem TLDR

Count hills and valleys base10 in a..b

Intuition

Brute-force

Approach

• Rust: itertools allows for tuple_windows

Complexity

• Time complexity: \(O(nlogn)\)

• Space complexity: \(O(logn)\)

Code

    fun totalWaviness(a: Int, b: Int) =
    (a..b).sumOf {"$it".windowed(3).count {(it[0]-it[1])*(it[2]-it[1])>0}}

    pub fn total_waviness(a: i32, b: i32) -> i32 {
        (a..=b).map(|x|x.to_string().bytes().tuple_windows()
        .filter(|(a,b,c)|a>b&&c>b||a<b&&c<b).count()as i32).sum::<i32>()
    }