【题目概要】
191. Number of 1 Bits Write a function that takes an unsigned integer and return the number of '1' bits it has (also known as the Hamming weight). Example 1: Input: 00000000000000000000000000001011 Output: 3 Explanation: The input binary string 00000000000000000000000000001011 has a total of three '1' bits.【思路分析】
计算位数上1的个数，直接用&运算即可，循环中用while比用for效率更好，较少n等于0后的不必要的运算【代码示例】
int hammingWeight(uint32_t n) { int count = 0; while(n) { if(n & 0x01) count++; n = n >> 1; } return count; }