338. 比特位计数

class Solution {
public:
    int countOnes(int x) 
    {
        int ones = 0;
        while (x > 0) 
        {
            x &= (x - 1);
            ones++;
        }
        return ones;
    }

    vector<int> countBits(int num) 
    {
        vector<int> bits(num + 1);
        for (int i = 0; i <= num; i++) 
        {
            bits[i] = countOnes(i);
        }
        return bits;
    }
};

//动态规划
class Solution 
{
public:
    vector<int> countBits(int num) 
    {
        vector<int> ans(num+1,0);
        for(int i =1;i<=num;i++)
        {
            ans[i] = ans[i&(i-1)]+1;
        }
        return ans;
    }
};