2026/03/26

[LeetCode] 338 Counting Bits 

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