190. Reverse Bits(Solution || Leetcode easy || Java)

Reverse bits of a given 32 bits unsigned integer.

Note:

• Note that in some languages, such as Java, there is no unsigned integer type. In this case, both input and output will be given as a signed integer type. They should not affect your implementation, as the integer’s internal binary representation is the same, whether it is signed or unsigned.
• In Java, the compiler represents the signed integers using 2’s complement notation. Therefore, in Example 2 above, the input represents the signed integer -3 and the output represents the signed integer -1073741825.

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)
Explanation: The input binary string 11111111111111111111111111111101 represents the unsigned integer 4294967293, so return 3221225471 which its binary representation is 10111111111111111111111111111111.

Constraints:

• The input must be a binary string of length 32

SOLUTION:

public class Solution {
    // you need treat n as an unsigned value
    public int reverseBits(int n) {
        //Create a integer to store answer
       int ans = 0;

       //run the loop 32 times as it is given in constraints that
       //the int is 32 bit long
        for(int i = 0; i < 32; i++){

            //append the last bit of integer to reverse it
           ans |= (n & 1);
           
           //this condition is necessary anotherwise the loop will
           // add a extra zero
            if(i != 31)

            //left shift ans to store next bit
            ans = ans << 1;

            //as the last bit is stored in ans remove that bit
            n = n >> 1;
        }

        return ans;
    }
}

Runtime 1 ms

Beats

97.45%

Memory 42.6 MB

Beats

34.36%

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