338. Counting Bits

338. Counting Bits

• 題目描述：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 should return [0,1,1,2,1,2].

• 題目大意：給定一個數字，找出0到這個數字之前每個數中二進制中1的個數，存放到數組中，並返回

• 思路：1的個數等於除了最低位1的個數加上最低位1的個數

• 代碼

  package DP;
  
  /**
  * @author OovEver
  * 2018/1/3 16:40
  * 1的個數等於除了最低位1的個數加上最低位1的個數
  */
  public class LeetCode338 {
    public int[] countBits(int num) {
        int[] res = new int[num + 1];
        res[0] = 0;
        for(int i=1;i<num+1;i++) {
            res[i] = res[i / 2] + i % 2;
        }
        return res;
    }
  }