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| 1 | +# [Problem 3314: Construct the Minimum Bitwise Array I](https://leetcode.com/problems/construct-the-minimum-bitwise-array-i/description/?envType=daily-question) |
| 2 | + |
| 3 | +## Initial thoughts (stream-of-consciousness) |
| 4 | +We need, for each given prime nums[i], to find the smallest nonnegative integer a such that a OR (a+1) == nums[i], otherwise output -1. A few quick observations: |
| 5 | +- nums[i] are small (<= 1000) and there are at most 100 numbers, so a direct search per number is feasible. |
| 6 | +- The operation a | (a+1) depends only on a's low bits (how many trailing 1s it has), but deriving a closed-form for every possible output value is a bit fiddly. Given the constraints, brute force search for the minimal a is simple and efficient. |
| 7 | +- Note: nums[i] = 2 (the only even prime) is impossible because for any a, a|(a+1) is >= 3? (in practice we will just test and get no hits -> -1). |
| 8 | + |
| 9 | +## Refining the problem, round 2 thoughts |
| 10 | +Refine to a straightforward algorithm: |
| 11 | +- For each target p in nums, iterate a from 0 up to p (or p+1) and test a | (a+1) == p. |
| 12 | +- Once we find the first such a, that's the minimal by construction; otherwise assign -1. |
| 13 | +Edge cases: |
| 14 | +- p = 2 should return -1 (no a satisfies condition). |
| 15 | +- p up to 1000 means checking up to ~1001 candidates per p is cheap. |
| 16 | +Time complexity: O(n * M) where M = max(nums) <= 1000, n <= 100 → at most ~100k iterations of a tiny constant-time bit op. Space: O(n) for result. |
| 17 | + |
| 18 | +This direct search is simple, robust, and efficient enough for constraints. |
| 19 | + |
| 20 | +## Attempted solution(s) |
| 21 | +```python |
| 22 | +from typing import List |
| 23 | + |
| 24 | +class Solution: |
| 25 | + def minimumBitwise(self, nums: List[int]) -> List[int]: |
| 26 | + res = [] |
| 27 | + for p in nums: |
| 28 | + found = -1 |
| 29 | + # search minimal a such that a | (a+1) == p |
| 30 | + # a cannot be much bigger than p, so iterate 0..p (inclusive) |
| 31 | + for a in range(0, p + 1): |
| 32 | + if (a | (a + 1)) == p: |
| 33 | + found = a |
| 34 | + break |
| 35 | + res.append(found) |
| 36 | + return res |
| 37 | + |
| 38 | +# Example usage: |
| 39 | +# s = Solution() |
| 40 | +# print(s.minimumBitwise([2,3,5,7])) # [-1,1,4,3] |
| 41 | +# print(s.minimumBitwise([11,13,31])) # [9,12,15] |
| 42 | +``` |
| 43 | + |
| 44 | +- Notes about the approach: |
| 45 | + - We simply brute-force each possible a from 0 to p and check the bitwise condition; the first match is the minimal a. |
| 46 | + - Time complexity: O(n * M) where n = len(nums) and M = max(nums) (M <= 1000). This is well within limits. |
| 47 | + - Space complexity: O(n) for the output list. |
| 48 | + - Implementation detail: iterating up to p is safe because a | (a+1) grows with a and will not produce values much larger than a+1; checking up to p is enough to find a solution if one exists for target p. |
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