Number of 1 bits

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.

求给定无符号数中1的出现次数，比如11的二进制00000000000000000000000000001011中包含3个1，则返回3

这道题用Java解需要非常小心，因为Java没有无符号int

如果是C语言的话可以循环n>0然后不断右移n并且判断最低位&1==1来给计数器加一。 Java中需要一些技巧。n & (n-1)可以用来消除最低位上的1，由此我们来判断计数器是否加一。

public int hammingWeight(int n) {
    if (n == 0) return 0;
    int result = 0;
    while (n != 0) {
        n&=(n-1);
        result++;
    }
    return result;
}