Create alternating-groups-i.py

Author: kamyu104

Python/alternating-groups-i.py

@@ -0,0 +1,31 @@
+# Time:  O(n)
+# Space: O(1)
+
+# sliding window, two pointers
+class Solution(object):
+    def numberOfAlternatingGroups(self, colors):
+        """
+        :type colors: List[int]
+        :rtype: int
+        """
+        k = 3
+        result = curr = left = 0
+        for right in xrange(len(colors)+k-1):  
+            if right-left+1 == k:
+                result += int(curr == k-1)
+                curr -= int(colors[left] != colors[(left+1)%len(colors)])
+                left += 1
+            curr += int(colors[right%len(colors)] != colors[(right+1)%len(colors)])
+        return result
+
+
+# Time:  O(n)
+# Space: O(1)
+# sliding window
+class Solution2(object):
+    def numberOfAlternatingGroups(self, colors):
+        """
+        :type colors: List[int]
+        :rtype: int
+        """
+        return sum(colors[i] != colors[(i+1)%len(colors)] != colors[(i+2)%len(colors)] for i in xrange(len(colors)))