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Monday, March 9, 2015

Hamming weights

Write a function that takes an unsigned integer and returns the number of ’1' bits it has (also known as the Hamming weight).
For example, the 32-bit integer ’11' has binary representation 00000000000000000000000000001011, so the function should return 3.
Well, all I can say is, see Wikipedia.


public class Solution {
    // you need to treat n as an unsigned value
    public int hammingWeight(int i) {
        i = i - ((i >> 1) & 0x55555555);
        i = (i & 0x33333333) + ((i >> 2) & 0x33333333);
        return (((i + (i >> 4)) & 0x0F0F0F0F) * 0x01010101) >> 24;
    }
}

I do have an easier approach, apparently LeetCode doesn't accept it.


public int hammingWeight(int n) {
        int ones = 0;
        while(n > 0){
            if((n & 1) > 0)
                ones++;
            n = (n >> 1);
        }
        return ones;
    }

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