Create number-of-substrings-containing-all-three-characters.py

Author: kamyu104

Python/number-of-substrings-containing-all-three-characters.py

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+# Time:  O(n)
+# Space: O(1)
+
+class Solution(object):
+    def numberOfSubstrings(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        result, left = 0, [-1]*3
+        for right, c in enumerate(s):
+            left[ord(c)-ord('a')] = right
+            result += min(left)+1
+        return result
+
+
+# Time:  O(n)
+# Space: O(1)
+class Solution2(object):
+    def numberOfSubstrings(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        result, left, count = 0, 0, [0]*3
+        for right, c in enumerate(s):
+            count[ord(s[right])-ord('a')] += 1
+            while all(count):
+                count[ord(s[left])-ord('a')] -= 1
+                left += 1
+            result += left
+        return result
+
+
+# Time:  O(n)
+# Space: O(1)
+class Solution3(object):
+    def numberOfSubstrings(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        result, right, count = 0, 0, [0]*3
+        for left, c in enumerate(s):
+            while right < len(s) and not all(count):
+                count[ord(s[right])-ord('a')] += 1
+                right += 1
+            if all(count):
+                result += (len(s)-1) - (right-1) + 1
+            count[ord(c)-ord('a')] -= 1
+        return result