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0190 - Reverse Bits

🧠 Idea

We need to reverse the bits of a 32-bit unsigned integer n.

👉 The trick is to process each bit from the least significant to the most significant, and construct the reversed number by shifting res left and adding the current bit of n.

🛠️ Key Points

  • Iterate 32 times (for each bit in a 32-bit integer).
  • res <<= 1 → make space for the next bit.
  • res += n & 1 → add the least significant bit of n to res.
  • n >>= 1 → move to the next bit of n.

💡 Intuition

Think of it as building the reversed number bit by bit:

  • Take the rightmost bit of n and append it to the left of res.
  • Repeat until all bits are processed.

⏱️ Complexity

  • Time: O(32) → constant, since we always process 32 bits.
  • Space: O(1), constant auxiliary space.