countBits.cpp

class Solution {
public:
    vector<int> countBits(int n) {
        vector<int> ans(n + 1, 0);
        for (int i = 1; i <= n; i++) {
            if (i & 1) ans[i] = ans[i - 1] + 1;
            else ans[i] = ans[i >> 1];
        }
        return ans;
    }
};

// O(nlogn) Brian Kernighan
class Solution {
public:
    int countOnes(int x) {
        int ones = 0;
        while (x > 0) {
            x &= (x - 1);
            ones++;
        }
        return ones;
    }

    vector<int> countBits(int n) {
        vector<int> bits(n + 1);
        for (int i = 0; i <= n; i++) {
            bits[i] = countOnes(i);
        }
        return bits;
    }
};

// 作者：LeetCode-Solution
// 链接：https://leetcode-cn.com/problems/counting-bits/solution/bi-te-wei-ji-shu-by-leetcode-solution-0t1i/
// 来源：力扣（LeetCode）
// 著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。