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3206. Alternating Groups I 👍

  • Time: $O(n)$
  • Space: $O(1)$
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class Solution {
 public:
  int numberOfAlternatingGroups(vector<int>& colors) {
    const int n = colors.size();
    int ans = 0;

    for (int i = 0; i < n; ++i)
      if (colors[i] != colors[(i - 1 + n) % n] &&
          colors[i] != colors[(i + 1) % n])
        ++ans;

    return ans;
  }
};

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class Solution {
  public int numberOfAlternatingGroups(int[] colors) {
    final int n = colors.length;
    int ans = 0;

    for (int i = 0; i < n; ++i)
      if (colors[i] != colors[(i - 1 + n) % n] && colors[i] != colors[(i + 1) % n])
        ++ans;

    return ans;
  }
}

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class Solution:
  def numberOfAlternatingGroups(self, colors: list[int]) -> int:
    n = len(colors)
    return sum(colors[i] != colors[i - 1] and
               colors[i] != colors[(i + 1) % n]
               for i in range(n))