338 、DP 统计从0到n每个数的二进制写法的1的个数

状态转移 dp[i] = dp[i>>1] + (i&1).

class Solution(object):
    def countBits(self, num):
        """
        :type num: int
        :rtype: List[int]
        """     
        dp = [0]*(1+num)
        for i in range(1,num+1):
            dp[i] = dp[i>>1]+(i&1)
        return dp