LeetCode-in-Java
190. Reverse Bits
Easy
Reverse bits of a given 32 bits unsigned integer.
Note:
- Note that in some languages, such as Java, there is no unsigned integer type. In this case, both input and output will be given as a signed integer type. They should not affect your implementation, as the integer’s internal binary representation is the same, whether it is signed or unsigned.
- In Java, the compiler represents the signed integers using 2’s complement notation. Therefore, in Example 2 above, the input represents the signed integer
-3and the output represents the signed integer-1073741825.
Example 1:
Input: n = 00000010100101000001111010011100
Output: 964176192 (00111001011110000010100101000000)
Explanation: The input binary string 00000010100101000001111010011100 represents the unsigned integer 43261596, so return 964176192 which its binary representation is 00111001011110000010100101000000.
Example 2:
Input: n = 11111111111111111111111111111101
Output: 3221225471 (10111111111111111111111111111111)
Explanation: The input binary string 11111111111111111111111111111101 represents the unsigned integer 4294967293, so return 3221225471 which its binary representation is 10111111111111111111111111111111.
Constraints:
- The input must be a binary string of length
32
Follow up: If this function is called many times, how would you optimize it?
Solution
public class Solution {
// you need treat n as an unsigned value
public int reverseBits(int n) {
int ret = 0;
// because there are 32 bits in total
for (int i = 0; i < 32; i++) {
ret = ret << 1;
// If the bit is 1 we OR it with 1, ie add 1
if ((n & 1) > 0) {
ret = ret | 1;
}
n = n >>> 1;
}
return ret;
}
}