Reverse Bits - The Coding Shala

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 In this post, we will learn how to Reverse Bits and will implement its solution in Java.

Reverse Bits Problem

Reverse bits of a given 32 bits unsigned integer.

Example 1:
Input: n = 00000010100101000001111010011100
Output:    964176192 (00111001011110000010100101000000)
Explanation: The input binary string 00000010100101000001111010011100 represents the unsigned integer 43261596, so return 964176192 which its binary representation is 00111001011110000010100101000000.

Example 2:
Input: n = 11111111111111111111111111111101
Output:   3221225471 (10111111111111111111111111111111)

Reverse Bits Java Solution

Approach 1

We will reverse bit by using shift operation. Will do this in two steps.

Step 1: Find the current bit.
Step 2: Set it to the 31-i position. [i is from 0 to 31].

Time Complexity: O(1). (loop will execute 32 times only)
Space Complexity: O(1).

Java Program: 

public class Solution {
    // you need treat n as an unsigned value
    public int reverseBits(int n) {
        int ans = 0;
        for(int i=0; i<32; i++) {
            //get the bit
            int bit = (n >> i) & 1;
            //set its position
            ans = ans | (bit << (31-i));
        }
        return ans;
    }
}


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