Reverse Bits
Source
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?
Java
public int reverseBits(int n) {
int result=0;
for(int i=0; i<32; i++){
result += n&1;
n>>=1;
if(i<31){
result <<=1;
}
}
return result;
}
private final Map<Byte, Integer> cache = new HashMap<Byte, Integer>();
public int reverseBits(int n) {
byte[] bytes = new byte[4];
for (int i = 0; i < 4; i++)
bytes[i] = (byte)((n >>> 8*i) & 0xFF);
int result = 0;
for (int i = 0; i < 4; i++) {
result += reverseByte(bytes[i]);
if (i < 3)
result <<= 8;
}
return result;
}
private int reverseByte(byte b) {
Integer value = cache.get(b);
if (value != null)
return value;
value = 0;
for (int i = 0; i < 8; i++) {
value += ((b >>> i) & 1);
if (i < 7)
value <<= 1;
}
cache.put(b, value);
return value;
}