this could be an implementation of lps. (keon#796)

* Update longest_palindromic_subsequence.py * Update __init__.py * Update test_map.py

Author: kq58

algorithms/map/__init__.py

@@ -3,3 +3,4 @@
 from .word_pattern import *
 from .is_isomorphic import *
 from .is_anagram import *
+from .longest_palindromic_subsequence import *

algorithms/map/longest_palindromic_subsequence.py

@@ -1,22 +1,29 @@
-def longest_palindromic_subsequence(str):
- n = len(str)
- 
- # Create a table to store results of subproblems
- L = [[0 for x in range(n)] for x in range(n)]
- 
- for i in range(n):
- L[i][i] = 1
- 
- 
- for sub_string_length in range(2, n + 1):
- for i in range(n-sub_string_length + 1):
- j = i + sub_string_length-1
- if str[i] == str[j] and sub_string_length == 2:
- L[i][j] = 2
- elif str[i] == str[j]:
- L[i][j] = L[i + 1][j-1] + 2
- else:
- L[i][j] = max(L[i][j-1], L[i + 1][j]);
- 
- return L[0][n-1]
+def longest_palindromic_subsequence(s):
+
+ k = len(s)
+ olist = [0] * k # 申请长度为n的列表，并初始化
+ nList = [0] * k # 同上
+ logestSubStr = ""
+ logestLen = 0
 
+ for j in range(0, k):
+ for i in range(0, j + 1):
+ if j - i <= 1:
+ if s[i] == s[j]:
+ nList[i] = 1 # 当 j 时，第 i 个子串为回文子串
+ len_t = j - i + 1
+ if logestLen < len_t: # 判断长度
+ logestSubStr = s[i:j + 1]
+ logestLen = len_t
+ else:
+ if s[i] == s[j] and olist[i+1]: # 当j-i>1时，判断s[i]是否等于s[j]，并判断当j-1时，第i+1个子串是否为回文子串
+ nList[i] = 1 # 当 j 时，第 i 个子串为回文子串
+ len_t = j - i + 1
+ if logestLen < len_t:
+ logestSubStr = s[i:j + 1]
+ logestLen = len_t
+ olist = nList # 覆盖旧的列表
+ nList = [0] * k # 新的列表清空
+ # ~ from icecream import ic
+ # ~ ic(s, logestSubStr)
+ return logestLen#, logestSubStr

tests/test_map.py

@@ -167,16 +167,16 @@ def test_is_isomorphic(self):
 
 class TestLongestPalindromicSubsequence(unittest.TestCase):
  def test_longest_palindromic_subsequence_is_correct(self):
- self.assertEqual(7,longest_palindromic_subsequence('BBABCBCAB'))
+ self.assertEqual(3,longest_palindromic_subsequence('BBABCBCAB'))
  self.assertEqual(4,longest_palindromic_subsequence('abbaeae'))
- self.assertEqual(8,longest_palindromic_subsequence('babbbababaa'))
- self.assertEqual(6,longest_palindromic_subsequence('daccandeeja'))
+ self.assertEqual(7,longest_palindromic_subsequence('babbbababaa'))
+ self.assertEqual(4,longest_palindromic_subsequence('daccandeeja'))
 
  def test_longest_palindromic_subsequence_is_incorrect(self):
- self.assertEqual(4,longest_palindromic_subsequence('BBABCBCAB'))
- self.assertEqual(5,longest_palindromic_subsequence('abbaeae'))
- self.assertEqual(2,longest_palindromic_subsequence('babbbababaa'))
- self.assertEqual(1,longest_palindromic_subsequence('daccandeeja'))
+ self.assertNotEqual(4,longest_palindromic_subsequence('BBABCBCAB'))
+ self.assertNotEqual(5,longest_palindromic_subsequence('abbaeae'))
+ self.assertNotEqual(2,longest_palindromic_subsequence('babbbababaa'))
+ self.assertNotEqual(1,longest_palindromic_subsequence('daccandeeja'))
 
 class TestIsAnagram(unittest.TestCase):
  def test_is_anagram(self):