Create find-substring-with-given-hash-value.py

Author: kamyu104

Python/find-substring-with-given-hash-value.py

@@ -0,0 +1,23 @@
+# Time:  O(n)
+# Space: O(1)
+
+# rolling hash
+class Solution(object):
+    def subStrHash(self, s, power, modulo, k, hashValue):
+        """
+        :type s: str
+        :type power: int
+        :type modulo: int
+        :type k: int
+        :type hashValue: int
+        :rtype: str
+        """
+        h, idx = 0, -1
+        pw = pow(power, k-1, modulo)
+        for i in reversed(xrange(len(s))):
+            if i+k < len(s):
+                h = (h-(ord(s[i+k])-ord('a')+1)*pw)%modulo
+            h = (h*power+(ord(s[i])-ord('a')+1))%modulo
+            if h == hashValue:
+                idx = i
+        return s[idx:idx+k]