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66. Plus One

  • Time: $O(n)$
  • Space: $O(1)$
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class Solution {
 public:
  vector<int> plusOne(vector<int>& digits) {
    for (int i = digits.size() - 1; i >= 0; --i) {
      if (digits[i] < 9) {
        ++digits[i];
        return digits;
      }
      digits[i] = 0;
    }

    digits.insert(digits.begin(), 1);
    return digits;
  }
};

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class Solution {
  public int[] plusOne(int[] digits) {
    for (int i = digits.length - 1; i >= 0; i--) {
      if (digits[i] < 9) {
        ++digits[i];
        return digits;
      }
      digits[i] = 0;
    }

    int[] ans = new int[digits.length + 1];
    ans[0] = 1;
    return ans;
  }
}

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class Solution:
  def plusOne(self, digits: list[int]) -> list[int]:
    for i, d in reversed(list(enumerate(digits))):
      if d < 9:
        digits[i] += 1
        return digits
      digits[i] = 0

    return [1] + digits