Create permutation-in-string.py

Author: kamyu104

Python/permutation-in-string.py

@@ -0,0 +1,39 @@
+# Time:  O(n)
+# Space: O(1)
+
+# Given two strings s1 and s2, write a function to return true
+# if s2 contains the permutation of s1. In other words,
+# one of the first string's permutations is the substring of the second string.
+#
+# Example 1:
+# Input:s1 = "ab" s2 = "eidbaooo"
+# Output:True
+# Explanation: s2 contains one permutation of s1 ("ba").
+# Example 2:
+# Input:s1= "ab" s2 = "eidboaoo"
+# Output: False
+# Note:
+# The input strings only contain lower case letters.
+# The length of both given strings is in range [1, 10,000].
+
+class Solution(object):
+    def checkInclusion(self, s1, s2):
+        """
+        :type s1: str
+        :type s2: str
+        :rtype: bool
+        """
+        counts = collections.Counter(s1)
+        l = len(s1)
+        for i in xrange(len(s2)):
+            if counts[s2[i]] > 0:
+                l -= 1
+            counts[s2[i]] -= 1
+            if l == 0:
+                return True
+            start = i + 1 - len(s1)
+            if start >= 0:
+                counts[s2[start]] += 1
+                if counts[s2[start]] > 0:
+                    l += 1
+        return False