Add longest palindrome code

dotfiles/lib/python/longest_palindrome.py

@@ -0,0 +1,90 @@
+#!/usr/bin/env python
+import sys
+from cached_property import cached_property
+
+
+class PalindromeSubstringFinder(object):
+
+    def __init__(self, input_string):
+        self.input_string = input_string
+        self.input_length = len(input_string)
+        self.position_count = (len(input_string) * 2) - 1
+        self._palindrome_lengths = [0] * self.position_count
+        self._total_comparisons = 0
+        self._max_palindrome_index = 0
+
+    @property
+    def longest_palindrome(self):
+        index = self._max_palindrome_index // 2
+        half_length = self.longest_palindrome_length // 2
+        offset =  self.longest_palindrome_length % 2
+        left_index = index - half_length + 1 - offset
+        right_index = index + half_length + 1
+        return self.input_string[left_index:right_index]
+
+    @property
+    def longest_palindrome_length(self):
+        return self._palindrome_lengths[self._max_palindrome_index]
+
+    def print_current_state(self, position):
+        print ("".join(map(str, self._palindrome_lengths)))
+        print (" ".join(self.input_string))
+        print ("{0}^".format(" " * position))
+
+    def palindrome_lengths(self):
+        if self.input_string is None or self.input_length < 1:
+            return []
+        max_reach = -1
+        for position in range(self.position_count):
+            starting_offset = self._palindrome_lengths[position] // 2
+            index = position // 2
+            right_offset = position % 2
+
+            palindrome_length, max_index = self.get_length_from_indices(
+                index - starting_offset,
+                index + starting_offset + right_offset,
+            )
+
+            self._palindrome_lengths[position] = palindrome_length
+
+            if palindrome_length > self._palindrome_lengths[self._max_palindrome_index]:
+                self._max_palindrome_index = position
+
+            if max_reach < max_index:
+                max_reach = max_index
+                self.copy_palindrome_lengths(position, palindrome_length)
+
+            self.print_current_state(position)
+
+        return self._palindrome_lengths
+
+    def copy_palindrome_lengths(self, position, palindrome_length):
+        # b a a b a a b
+        # 1004007004001
+        for offset in range(1, palindrome_length - 1):
+            self._palindrome_lengths[position + offset] = (
+                min(
+                    self._palindrome_lengths[position - offset],
+                    palindrome_length - offset
+                )
+            )
+
+    def get_length_from_indices(self, left_index, right_index):
+        while (left_index >= 0 and right_index < self.input_length and
+               self.input_string[left_index] == self.input_string[right_index]):
+            self._total_comparisons += 1
+            left_index -= 1
+            right_index += 1
+        self._total_comparisons += 1
+        # We'll always go one set of indices PAST the point that we should have,
+        # so right_index - left_index + 1 becomes the below:
+        return right_index - left_index - 1, right_index - 1
+
+
+if __name__ == '__main__':
+    target = sys.argv[1]
+    finder = PalindromeSubstringFinder(target)
+    finder.palindrome_lengths()
+    print(finder._total_comparisons)
+    print(finder._max_palindrome_index)
+    print(finder.longest_palindrome)