題目：191. Number of 1 Bits

連結：https://leetcode.com/problems/number-of-1-bits/description/

• 等級：Easy

class Solution {
    public int hammingWeight(int n) {
        
        int count = 0;

        while (n != 0) {
            
            if ((n & 1) == 1)
                count++;
            
            n = n >>> 1;
        }
            
        return count;
    }
}

• Time complexity: O(n)
• Space complexity: O(1)

題目：190. Reverse Bits

連結：https://leetcode.com/problems/reverse-bits/description/

• 等級：Easy
• The input must be a binary string of length 32

class Solution {
    
    public int reverseBits(int num) {
        
        num = ((num & 0xffff0000) >>> 16) | ((num & 0x0000ffff) << 16);
        num = ((num & 0xff00ff00) >>> 8) | ((num & 0x00ff00ff) << 8);
        num = ((num & 0xf0f0f0f0) >>> 4) | ((num & 0x0f0f0f0f) << 4);
        num = ((num & 0xcccccccc) >>> 2) | ((num & 0x33333333) << 2);
        num = ((num & 0xaaaaaaaa) >>> 1) | ((num & 0x55555555) << 1);
        
        return num;
        
    }
}

• Time complexity: O(1)
• Space complexity: O(1)