Create count-binary-substrings.py

Author: kamyu104

Python/count-binary-substrings.py

@@ -0,0 +1,42 @@
+# Time:  O(n)
+# Space: O(1)
+
+# Give a string s, count the number of non-empty (contiguous) substrings
+# that have the same number of 0's and 1's, and all the 0's and all the 1's
+# in these substrings are grouped consecutively.
+#
+# Substrings that occur multiple times are counted the number of times they occur.
+#
+# Example 1:
+# Input: "00110011"
+# Output: 6
+# Explanation: There are 6 substrings that have equal number of consecutive 1's and 0's:
+#              "0011", "01", "1100", "10", "0011", and "01".
+#
+# Notice that some of these substrings repeat and are counted the number of times they occur.
+#
+# Also, "00110011" is not a valid substring because all the 0's (and 1's) are not grouped together.
+# Example 2:
+# Input: "10101"
+# Output: 4
+# Explanation: There are 4 substrings: "10", "01", "10", "01" that have equal number of consecutive 1's and 0's.
+#       
+# Note:
+# s.length will be between 1 and 50,000.
+# s will only consist of "0" or "1" characters.
+
+class Solution(object):
+    def countBinarySubstrings(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        result, prev, curr = 0, 0, 1
+        for i in xrange(1, len(s)):
+            if s[i-1] != s[i]:
+                result += min(prev, curr)
+                prev, curr = curr, 1
+            else:
+                curr += 1
+        result += min(prev, curr)
+        return result