Create count-substrings-that-differ-by-one-character.py

Author: kamyu104

Python/count-substrings-that-differ-by-one-character.py

@@ -0,0 +1,22 @@
+# Time:  O(m * n)
+# Space: O(1)
+
+class Solution(object):
+    def countSubstrings(self, s, t):
+        """
+        :type s: str
+        :type t: str
+        :rtype: int
+        """
+        def count(i, j):  # for each possible alignment, count the number of substrs that differ by 1 char
+            result = left_cnt = right_cnt = 0  # left and right consecutive same counts relative to the different char
+            for k in xrange(min(len(s)-i, len(t)-j)):
+                right_cnt += 1
+                if s[i+k] != t[j+k]:
+                    left_cnt, right_cnt = right_cnt, 0
+                    # prev_i = i+k-prev+1
+                result += left_cnt  # target substrs are [s[left_i+c:i+k+1] for c in xrange(left_cnt)]
+            return result
+
+        return sum(count(i, 0) for i in xrange(len(s))) + \
+               sum(count(0, j) for j in xrange(1, len(t)))