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:
For num = 5 you should return [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.

 

代码：

/**
 * Return an array of size *returnSize.
 * Note: The returned array must be malloced, assume caller calls free().
 */
int *countBits(int n,int *returnSize)
{
    int *p = (int *) malloc(sizeof(int)*(n+1));
    *returnSize = n+1;
    int tmp = 2,i = 2;
    int *q = p;
    *q++ = 0;
    *q++ = 1;
    while(i<=n)
    {
        *q = *(q-tmp)+1;
        q++;
        i++;
        if(i%tmp == 0)
            tmp = tmp<<1;
    }
    return p;
}