LeetCode Entry

1461. Check If a String Contains All Binary Codes of Size K

23.02.2026 medium 2026 kotlin rust

All numbers as substring length of k window

1461. Check If a String Contains All Binary Codes of Size K medium blog post substack youtube

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Problem TLDR

All numbers as substring length of k #medium #sliding_window

Intuition

Use sliding window of k. Calculate the current number, add to a set. Uniqs count should be 2^k.

Approach

• use built-in windows, the k is small, can take substrings on the fly
• inverted solution: number of allowed duplicates is len-k+1 - 2^k
• return early

Complexity

• Time complexity: \(O(n)\)

• Space complexity: \(O(n)\)

Code

// 130ms
    fun hasAllCodes(s: String, k: Int) =
    s.windowed(k).toSet().size == 1 shl k

// 87ms
    pub fn has_all_codes(s: String, k: i32) -> bool {
        s.as_bytes().windows(k as usize).unique().count() as i32 == 1 << k
    }