# LeetCode – Reverse Bits (Java)

Problem

Reverse bits of a given 32 bits unsigned integer.

For example, given input 43261596 (represented in binary as 00000010100101000001111010011100), return 964176192 (represented in binary as 00111001011110000010100101000000).

Follow up:
If this function is called many times, how would you optimize it?

Related problem: Reverse Integer

Java Solution

 public int reverseBits(int n) { for (int i = 0; i < 16; i++) { n = swapBits(n, i, 32 - i - 1); }   return n; }   public int swapBits(int n, int i, int j) { int a = (n >> i) & 1; int b = (n >> j) & 1;   if ((a ^ b) != 0) { return n ^= (1 << i) | (1 << j); }   return n; }
Category >> Algorithms >> Interview >> Java
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• Zhongyuan Zhang

is this the optimised solution?

map = {0: 0, 1: 8, 2: 4, 3: 12, 4: 2, 5: 10, 6: 6, 7: 14, 8: 1, 9: 9, 10: 5, 11: 13, 12: 3, 13: 11, 14: 7, 15: 15}
res = 0
for i in range(8):
res <>= 4
return res

• Walden

public class Solution {
// you need treat n as an unsigned value
public int reverseBits(int n) {
int answer = 0;
for (int i = 0; i < 32; i++) {
answer <> x) & 1);
}
return answer;
}
}
this was a 2ms java solution