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1630. Arithmetic Subarrays 👍

  • Time: $O(mn)$
  • Space: $O(n)$
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class Solution {
 public:
  vector<bool> checkArithmeticSubarrays(vector<int>& nums, vector<int>& l,
                                        vector<int>& r) {
    vector<bool> ans;

    for (int i = 0; i < l.size(); ++i)
      ans.push_back(isArithmetic(nums, l[i], r[i]));

    return ans;
  }

 private:
  bool isArithmetic(vector<int>& nums, int l, int r) {
    if (r - l < 2)
      return true;

    unordered_set<int> numsSet;
    int mini = INT_MAX;
    int maxi = INT_MIN;

    for (int i = l; i <= r; ++i) {
      mini = min(mini, nums[i]);
      maxi = max(maxi, nums[i]);
      numsSet.insert(nums[i]);
    }

    if ((maxi - mini) % (r - l) != 0)
      return false;

    const int interval = (maxi - mini) / (r - l);

    for (int k = 1; k <= r - l; ++k)
      if (!numsSet.count(mini + k * interval))
        return false;

    return true;
  }
};

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class Solution {
  public List<Boolean> checkArithmeticSubarrays(int[] nums, int[] l, int[] r) {
    List<Boolean> ans = new ArrayList<>();

    for (int i = 0; i < l.length; ++i)
      ans.add(isArithmetic(nums, l[i], r[i]));

    return ans;
  }

  private boolean isArithmetic(int[] nums, int l, int r) {
    if (r - l < 2)
      return true;

    int min = Integer.MAX_VALUE;
    int max = Integer.MIN_VALUE;
    Set<Integer> numsSet = new HashSet<>();

    for (int i = l; i <= r; ++i) {
      min = Math.min(min, nums[i]);
      max = Math.max(max, nums[i]);
      numsSet.add(nums[i]);
    }

    if ((max - min) % (r - l) != 0)
      return false;

    final int interval = (max - min) / (r - l);

    for (int k = 1; k <= r - l; ++k)
      if (!numsSet.contains(min + k * interval))
        return false;

    return true;
  }
}

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class Solution:
  def checkArithmeticSubarrays(self, nums: List[int], l: List[int], r: List[int]) -> List[bool]:
    return [self._isArithmetic(nums, a, b) for a, b in zip(l, r)]

  def _isArithmetic(self, nums: List[int], l: int, r: int) -> bool:
    if r - l < 2:
      return True

    numsSet = set()
    mini = math.inf
    maxi = -math.inf

    for i in range(l, r+1):
      mini = min(mini, nums[i])
      maxi = max(maxi, nums[i])
      numsSet.add(nums[i])

    if (maxi - mini) % (r - l) != 0:
      return False

    interval = (maxi - mini) // (r - l)
    return all(mini + k * interval in numsSet
               for k in range(1, r - l + 1))