190. Reverse Bits

二刷 06/2022

Version #2

Time O(32)

Space O(1)

Runtime: 2 ms, faster than 27.48% of Java online submissions for Reverse Bits.

Memory Usage: 41.5 MB, less than 91.42% of Java online submissions for Reverse Bits.

public class Solution {

    // you need treat n as an unsigned value

    public int reverseBits(int n) {

        int result = 0;

        for (int i = 0; i < 32; i++) {

            result = (result << 1) + (n & 1);

            n >>>= 1;

        }

        return result;

    }

}

一刷

Version #2
12.19 %
public class Solution {
    // you need treat n as an unsigned value
    public int reverseBits(int n) {
        int result = 0;
        for (int i = 0; i < 32; i++) {
            result = (result << 1) | (n & 1);
            n >>>= 1;
        }
        return result;
    }
}


Version # 1 swap
28.24 %
public class Solution {
    // you need treat n as an unsigned value
    public int reverseBits(int n) {
        for (int i = 0; i < 16; i++) {
            n = swapBits(n, i, 32 - i - 1);
        }
        return n;
    }
    private 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;
    }
}