Swift 338. Counting Bits

概述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: For num = 5 you s

Given a non negative integer numbernum. For every numbersiin the range0 ≤ i ≤ numcalculate the number of 1's in their binary representation and return them as an array.

Example:
Fornum = 5you should return[0,1,2,2].

题意：给定num,计算从0到num中的每个数的二进制中1的个数

解题思路：分奇偶数进行处理，奇数n包含1的个数等于n/2 包含1的个数 +1,因为奇数的二进制的低位为1，除2之后相当于右移一位，少了一个1，所以要加1；同理，偶数不需要加1，等于n/2 包含1的个数

程序如下：

func countBits(num: Int) -> [Int] {            var arr:[Int] = [0]    if num == 0  {return arr}    for i in 1...num    {         if i%2 == 1        {            arr.append(arr[i/2]+1)        }else{            arr.append(arr[i/2])        }            }    return arr    }

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