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BitMagic_SwapAllOddEvenBits.java
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BitMagic_SwapAllOddEvenBits.java
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import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
// https://practice.geeksforgeeks.org/problems/swap-all-odd-and-even-bits/0
// https://www.geeksforgeeks.org/swap-all-odd-and-even-bits/
/*
Time Complexity: O(1), the time needed is constant since we iterate
through the same sized integer irrespective of its value.
Space Complexity: O(1)
1. Isolate even bit values by doing AND of input with 0xAAAAAAAA,
which has all even bits set to 1. Right shift this by 1 bit.
2. Isolate odd bit values by doing AND of input with 0x55555555,
which has all odd bits set to 1. Left shift this by 1 bit.
3. OR the above 2 values to combine them.
*/
// https://www.youtube.com/watch?v=PHH41vjQXrQ (A good animated explanation)
// https://www.youtube.com/watch?v=AVWaH9bzeYc
// https://www.youtube.com/watch?v=GWLCF808oVI
public class BitMagic_SwapAllOddEvenBits {
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int t = Integer.parseInt(br.readLine().trim());
while(t-->0) {
int n = Integer.parseInt(br.readLine().trim());
int evenBits = n & 0xAAAAAAAA; // extracting the even bits
int oddBits = n & 0x55555555; // extracting the odd bits
int swappedValue = (evenBits >> 1) | (oddBits << 1) ;
System.out.println(swappedValue);
}
}
}