Check if N and its Double Exist Problem & Solution

See the check if n and its double exist problem on LeetCode.

C++ Solution

#pragma GCC optimize("Ofast")
#pragma GCC optimization("unroll-loops")
#pragma GCC target("avx,avx2,fma")

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

class Solution {
public:
  bool checkIfExist(vector<int>& arr) {
    sort(arr.begin(), arr.end());
    for (int i = 0; i < arr.size(); ++i) {
      if (arr[i] >= 0) {
        if (binary_search(arr.begin() + i + 1, arr.end(), 2 * arr[i])) {
          return true;
        }
      } else if (binary_search(arr.begin(), arr.begin() + i, 2 * arr[i])) {
        return true;
      }
    }

    return false;
  }
};

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