add more problems

Author: LEUNGUU

easy/1143.longest_common_subsequence.py

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+# Longest Common Subsequence
+#
+# [Medium] [AC:58.4% 139K of 238K] [filetype:python3]
+#
+# Given two strings text1 and text2, return the length of their longest common subsequence.
+#
+# A subsequence of a string is a new string generated from the original string with some
+# characters(can be none) deleted without changing the relative order of the
+# remaining characters. (eg, "ace" is a subsequence of "abcde" while "aec" is
+# not). A common subsequence of two strings is a subsequence that is common to both strings.
+#
+# If there is no common subsequence, return 0.
+#
+# Example 1:
+#
+# Input: text1 = "abcde", text2 = "ace"
+#
+# Output: 3
+#
+# Explanation: The longest common subsequence is "ace" and its length is 3.
+#
+# Example 2:
+#
+# Input: text1 = "abc", text2 = "abc"
+#
+# Output: 3
+#
+# Explanation: The longest common subsequence is "abc" and its length is 3.
+#
+# Example 3:
+#
+# Input: text1 = "abc", text2 = "def"
+#
+# Output: 0
+#
+# Explanation: There is no such common subsequence, so the result is 0.
+#
+# Constraints:
+#
+# 1 <= text1.length <= 1000
+#
+# 1 <= text2.length <= 1000
+#
+# The input strings consist of lowercase English characters only.
+#
+# [End of Description]:
+# memo
+# key point is creating the dp array
+class Solution:
+    def longestCommonSubsequence(self, text1: str, text2: str) -> int:
+        memo = {}
+
+        def dp(i, j):
+            # base case
+            if i == -1 or j == -1:
+                return 0
+            if (i, j) in memo:
+                return memo[(i, j)]
+            if text1[i] == text2[j]:
+                # find the common character
+                memo[(i, j)] = dp(i - 1, j - 1) + 1
+                return memo[(i, j)]
+            else:
+                memo[(i, j)] = max(dp(i - 1, j), dp(i, j - 1))
+                return memo[(i, j)]
+
+        return dp(len(text1) - 1, len(text2) - 1)

easy/516.longest_palindromic_subsequence.py

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+# Longest Palindromic Subsequence
+#
+# [Medium] [AC:53.9% 132.1K of 245.3K] [filetype:python3]
+#
+# Given a string s, find the longest palindromic subsequence's length in s.
+# You may assume that the maximum length of s is 1000.
+#
+# Example 1:
+#
+# Input:
+#
+# "bbbab"
+#
+# Output:
+#
+# 4
+#
+# One possible longest palindromic subsequence is "bbbb".
+#
+# Example 2:
+#
+# Input:
+#
+# "cbbd"
+#
+# Output:
+#
+# 2
+#
+# One possible longest palindromic subsequence is "bb".
+#
+# Constraints:
+#
+# 1 <= s.length <= 1000
+#
+# s consists only of lowercase English letters.
+#
+# [End of Description]:
+class Solution:
+    def longestPalindromeSubseq(self, s: str) -> int:
+        pass