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).

O(n) time O(1) space

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public class Solution {
    // you need treat n as an unsigned value
    public int reverseBits(int n) {
        if (n == 0) return 0;
        int res = 0;
        for (int i = 0 ; i < 32; i++) {
            res <<= 1;
            res += n & 1;
            n >>= 1;
        }
        return res;
    }
}