題目：
Given a non negative integer number num. For every numbers i in the range 0 ≤ i ≤ num calculate the number of 1's in their binary representation and return them as an array.
Example 1:
Input: 2 Output: [0,1,1]
Example 2:
Input: 5
Output: [0,1,1,2,1,2]
翻譯：
給定一個非負的正數num。對於範圍 0到num 中的每一個數字i，計算這個數字的二進制表示中1的個數並將它們返回成一個數組。
例子 1:
輸入: 2 輸出: [0,1,1]
例子 2:
輸入: 5
輸出: [0,1,1,2,1,2]
思路：
參見http://www.cnblogs.com/grandyang/p/5294255.html，很全面很具體。
C++代碼（Visual Studio 2017）：
列出的是思路中方法四。
#include "stdafx.h"
#include <iostream>
#include <vector>
using namespace std;
class Solution {
public:
vector<int> countBits(int num) {
vector<int> res(num + 1,0 );
for (int i = 1; i <= num; i++) {
res[i] = res[i&(i - 1)] + 1;
}
return res;
}
};
int main()
{
Solution s;
int num = 5;
vector<int> res = s.countBits(num);
for (int i = 0; i < res.size(); i++) {
cout << res[i] << " ";
}
return 0;
}