338. Counting Bits

迷南。 2022-03-25 00:46 281阅读 0赞

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:

  1. Input: 2
  2. Output: [0,1,1]

Example 2:

  1. Input: 5
  2. Output: 
  3. [0,1,1,2,1,2]
  5. Follow up:
  • It is very easy to come up with a solution with run time O(n*sizeof(integer)). But can you do it in linear time O(n)/possibly in a single pass?
  • Space complexity should be O(n).

  • Can you do it like a boss? Do it without using any builtin function like __builtin_popcount in c++ or in any other language.

    class Solution {
    public:

    1. vector<int> countBits(int num) {
    2.    vector<int> res(num+1,0);
    3.     if(num<0)
    4.         return res;
    5.     for(int i=1;i<=num;i++){
    6.         res[i]=res[i&(i-1)]+1;
    7.     }
    8.     return res; 
    9. }

    };

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