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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.

位运算，找出int型数字为1的位的个数。因为是32位，外层循环有32次，但是一旦循环过的位数最大值大于当前值，就停止运算，因为之后的左移运算，全为0

int hammingWeight(uint32_t n) {
    int result = 0;
    int cursor = 1;
    for(int i = 1; i <= 32; i++)
    {
        if( (n & cursor) != 0)
        {
            result++;
        }
        cursor = cursor << 1;
        
        if(pow(2,i) - 1 >= n)
        {
            break;
        }
    }
    return result;
}

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原文地址：http://www.cnblogs.com/Anthony-Wang/p/5127257.html