add solution: longest-common-subsequence

Author: dusunax

longest-common-subsequence/dusunax.py

@@ -0,0 +1,27 @@
+'''
+# 1143. Longest Common Subsequence
+
+use DP table.
+
+> key: tuple(current index in text1, current index in text2)
+> value: LCS of text1[i:] and text2[j:]
+'''
+class Solution:
+    def longestCommonSubsequence(self, text1: str, text2: str) -> int:
+        dp = {}
+
+        def helper(i, j):
+            if i == len(text1) or j == len(text2):
+                return 0
+
+            if (i, j) in dp:
+                return dp[(i, j)]
+
+            if text1[i] == text2[j]:
+                dp[(i, j)] = 1 + helper(i + 1, j + 1)
+            else:
+                dp[(i, j)] = max(helper(i + 1, j), helper(i, j + 1))
+
+            return dp[(i, j)]
+
+        return helper(0, 0)