leetcode 338 counting bits

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:

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

Example 2:

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Input: 5
Output: [0,1,1,2,1,2]

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.

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import java.util.ArrayList;

public class {

* 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:
*
* Input: 2
* Output: [0,1,1]
* Example 2:
*
* Input: 5
* Output: [0,1,1,2,1,2]
* 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.
*/
public int[] countBits(int num) {
int[] dp = new int[num + 1];
dp[0] = 0;
int width = 1;
for (int i=1; i<=num; i++){
dp[i] = dp[i-width] + 1;
if (width == i){
width *= 2;
}
}
return dp;
}
}