LeetCode-338. Counting Bits
2016-04-17 16:55
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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
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.
这道题主要需要一个先验知识就是 n=n&(n-1)会消去n最后面的一个1;然后就是将每一个数与之前数相与,比如b = n&(n-1),那么n就比b多了一个1,而b比n小,b有几个1已知。
return them as an array.
Example:
For
num = 5you 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.
这道题主要需要一个先验知识就是 n=n&(n-1)会消去n最后面的一个1;然后就是将每一个数与之前数相与,比如b = n&(n-1),那么n就比b多了一个1,而b比n小,b有几个1已知。
public class Solution { public int[] countBits(int num) { int[] temp = new int[num+1]; temp[0] = 0; for(int i = 1; i <= num; i++){ temp[i] = 1 + temp[i&(i-1)]; } return temp; } }
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