191.Number of 1 Bits

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Bit Manipulation, Easy

Question

Write a function that takes an unsigned integer and returns the number of ‘1’ bits it has (also known as the Hamming weight).

Example 1:

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Input: 11
Output: 3
Explanation: Integer 11 has binary representation 00000000000000000000000000001011

Example 2:

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Input: 128
Output: 1
Explanation: Integer 128 has binary representation 00000000000000000000000010000000

My Answer

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public class Solution {
    // you need to treat n as an unsigned value
    public int hammingWeight(int n) {
        int res=0;
        while(n!=0){
            n = n & (n-1);
            res++;
        }
        return res;
    }
}

Running time: O(n), n is the length of the given number, 3ms

Other Answer

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public class Solution {
    // you need to treat n as an unsigned value
    public int hammingWeight(int n) {
        int res=0;
        while(n!=0){
            res += n & 1;
            n = n >>> 1;
        }
        return res;
    }
}

Running time: O(n), n is the length of the given number, 3ms