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268. Missing Number

  • Time: $O(n)$
  • Space: $O(1)$
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class Solution {
 public:
  int missingNumber(vector<int>& nums) {
    int ans = nums.size();

    for (int i = 0; i < nums.size(); ++i)
      ans ^= i ^ nums[i];

    return ans;
  }
};

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class Solution {
  public int missingNumber(int[] nums) {
    int ans = nums.length;

    for (int i = 0; i < nums.length; ++i)
      ans ^= i ^ nums[i];

    return ans;
  }
}

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class Solution:
  def missingNumber(self, nums: List[int]) -> int:
    ans = len(nums)

    for i, num in enumerate(nums):
      ans ^= i ^ num

    return ans