190. Reverse Bits

Reverse bits of a given 32 bits unsigned integer.

For example, given input 43261596 (represented in binary as 00000010100101000001111010011100), return 964176192 (represented in binary as00111001011110000010100101000000).

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

Related problem: Reverse Integer

两个指针i，j从前后向中间扫，如果bit[i] != bit[j]，反转bit[i]和bit[j].

public class Solution {
　　// you need treat n as an unsigned value
　　public int reverseBits(int n) {
　　　　for (int i = 0; i < 16; i++) {
　　　　　　n = swapBit(n, i, 31-i);
　　　　}
　　　　return n;
　　}

　　public int swapBit(int n, int i, int j) {
　　　　int low = (n >> i) & 1;
　　　　int high = (n >> j) & 1;
　　　　if ((low ^ high) == 1) {
　　　　　　n ^= 1 << i;
　　　　　　n ^= 1 << j;
　　　　}
　　　　return n;
　　}
}