Create Count Binary Substrings.py

Author: sugia

Count Binary Substrings.py

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+'''
+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
+        """
+        if len(s) < 2:
+            return 0
+        
+        res = 0
+        prev = 0
+        cur = 1
+        for i in xrange(1, len(s)):
+            if s[i] != s[i-1]:
+                res += min(prev, cur)
+                prev, cur = cur, 1
+            else:
+                cur += 1
+                
+        res += min(prev, cur)
+        return res