Counting Bits Problem & Solution

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.

See the counting bits problem on LeetCode.

C++ Solution

#pragma GCC optimize("Ofast")
#pragma GCC optimization("unroll-loops")

static const int _=[](){std::ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);return 0;}();

class Solution {
  vector<int> countBits(int n) {
    vector<int> results(n + 1, 0);

    for (int i = 1; i < results.size(); ++i) {
      results[i] = __builtin_popcount(i);

    return results;

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