Given an integer n, return an array ans of length n + 1 such that for each i (0 <= i <= n), ans[i] is the number of 1‘s in the binary representation of i.
Example 1:
Input: n = 2 Output: [0,1,1] Explanation: 0 --> 0 1 --> 1 2 --> 10
Example 2:
Input: n = 5 Output: [0,1,1,2,1,2] Explanation: 0 --> 0 1 --> 1 2 --> 10 3 --> 11 4 --> 100 5 --> 101
Constraints:
0 <= n <= 105
Follow up:
O(n log n). Can you do it in linear time O(n) and possibly in a single pass?__builtin_popcount in C++)?
class Solution {
public:
vector<int> countBits(int n) {
if(n==0)return {0};
vector<int> ans(n+1,0);
ans[1]=1;
for(int i=2; i<=n; i++)
{
if(i%2==0)ans[i]=ans[i/2];
else ans[i]=ans[i/2]+1;
}
return ans;
}
};
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