98 lines
2.4 KiB
Markdown
98 lines
2.4 KiB
Markdown
# Leetcode Reverse-Bits
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#### 2022-07-22 15:15
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> ##### Algorithms:
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> #algorithm #bit_manipulation
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> ##### Data structures:
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> #DS #bitset
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> ##### Difficulty:
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> #coding_problem #difficulty-easy
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> ##### Additional tags:
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> #leetcode
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> ##### Revisions:
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> N/A
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##### Related topics:
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```expander
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tag:#bitset
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```
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##### Links:
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- [Link to problem](https://leetcode.com/problems/reverse-bits/)
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- [Solution and detailed explanation](https://leetcode.com/problems/reverse-bits/discuss/1232842/JAVA-C%2B%2B-%3A-0ms-or-O(1)-Time-Complexity-or-in-place-or-Detailed-Explanation)
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- [Shifting solution an explanation](https://leetcode.com/problems/reverse-bits/discuss/54741/O(1)-bit-operation-C++-solution-(8ms)/301342)
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___
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### Problem
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Reverse bits of a given 32 bits unsigned integer.
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#### Examples
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**Example 1:**
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**Input:** n = 00000010100101000001111010011100
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**Output:** 964176192 (00111001011110000010100101000000)
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**Explanation:** The input binary string **00000010100101000001111010011100** represents the unsigned integer 43261596, so return 964176192 which its binary representation is **00111001011110000010100101000000**.
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**Example 2:**
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**Input:** n = 11111111111111111111111111111101
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**Output:** 3221225471 (10111111111111111111111111111111)
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**Explanation:** The input binary string **11111111111111111111111111111101** represents the unsigned integer 4294967293, so return 3221225471 which its binary representation is **10111111111111111111111111111111**.
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#### Constraints
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- The input must be a **binary string** of length `32`
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### Thoughts
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> [!summary]
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> This is a #bit_manipulation problem.
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There are two methods:
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- swapping bits inside the bitset
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- shifting
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#### Method 1: Swapping
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This is the most simple and intuitive one, all you have to do is swap the first and last numbers, and continue like that.
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#### Method 2: Shifting
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The bitset has operations like this `<<` `>>`, which can be used to shift, and reverse the array.
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The operation is already documented in the link above:
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[[Leetcode Reverse-Bits#Links]]
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### Solution
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#### Method 1:
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```cpp
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class Solution {
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public:
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uint32_t reverseBits(uint32_t n) {
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// swap bits inside the function
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bitset<32> nb(n);
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bool tmp;
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int l = 0, r = 31;
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while (l < r) {
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tmp = nb[l];
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nb[l] = nb[r];
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nb[r] = tmp;
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l++;
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r--;
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}
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return nb.to_ulong();
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}
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};
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```
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#### Shifting:
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==#TODO solve it using shifting== |