LeetCode Entry

190. Reverse Bits

16.02.2026 easy 2026 kotlin rust

Reverse bits

190. Reverse Bits easy blog post substack youtube

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Problem TLDR

Reverse bits #easy #bits

Intuition

Manually reverse all 31 positions.

Approach

• if called many times: use built-in functions (they should be optimized and cached) and use lookup tables if memory allows

Complexity

• Time complexity: \(O(log(n))\)

• Space complexity: \(O(1)\)

Code

// 103ms
    fun reverseBits(n: Int) =
        Integer.reverse(n)
        /*
        (0..31).sumOf { b -> n shr b and 1 shl (31-b) }
        n.toString(2).reversed().padEnd(32,'0').toInt(2)
        (0..31).fold(0) { r, b -> n shr b and 1 shl (31-b) or r }
         */

// 2ms
    pub const reverse_bits: fn(i32) -> i32 = i32::reverse_bits;
    /*
    pub fn reverse_bits(n: i32) -> i32 {
        (0..32).map(|b| (n >> b & 1) << (31-b)).sum()
    }
    */