[338] Counting Bits

ㄜ.......

雖然是無痛PASS了，但是看不懂別人的 

while (temp)

{

    count++;

    temp= temp & (temp-1) ;

}

是怎麼辦到的  XD

/**

* Note: The returned array must be malloced, assume caller calls free().

*/

int count(int n)

{

int ret=0;

while (n>0)

{

ret += (n & 1);

n=n>>1;

}

return ret;

}

int* countBits(int n, int* returnSize){

*returnSize= n+1;

int *ret = malloc (sizeof(int)*(n+1));

for (int i=0;i<=n;i++)

{

ret[i]=count(i);

}

return ret;

}

ps. 可以縮短成

/**

* Note: The returned array must be malloced, assume caller calls free().

*/

int* countBits(int n, int* returnSize){

*returnSize= n+1;

int *ret = calloc (n+1, sizeof(int));

for (int i=0;i<=n;i++)

{

int tmp=i;

while (tmp>0)

{

ret[i] += (tmp & 1);

tmp=tmp>>1;

}

}

return ret;

}