Create shortest-common-supersequence.py

Author: kamyu104

Python/shortest-common-supersequence.py

@@ -0,0 +1,37 @@
+# Time:  O(m * n)
+# Space: O(m * n)
+
+class Solution(object):
+    def shortestCommonSupersequence(self, str1, str2):
+        """
+        :type str1: str
+        :type str2: str
+        :rtype: str
+        """
+        dp = [[0 for _ in xrange(len(str2)+1)] for _ in xrange(2)]
+        bt = [[None for _ in xrange(len(str2)+1)] for _ in xrange(len(str1)+1)]
+        for i, c in enumerate(str1):
+            bt[i+1][0] = (i, 0, c)
+        for j, c in enumerate(str2):
+            bt[0][j+1] = (0, j, c)
+        for i in xrange(len(str1)):
+            for j in xrange(len(str2)):
+                if dp[i % 2][j+1] > dp[(i+1) % 2][j]:
+                    dp[(i+1) % 2][j+1] = dp[i % 2][j+1]
+                    bt[i+1][j+1] = (i, j+1, str1[i])
+                else:
+                    dp[(i+1) % 2][j+1] = dp[(i+1) % 2][j]
+                    bt[i+1][j+1] = (i+1, j, str2[j])
+                if str1[i] != str2[j]:
+                    continue
+                if dp[i % 2][j]+1 > dp[(i+1) % 2][j+1]:
+                    dp[(i+1) % 2][j+1] = dp[i % 2][j]+1
+                    bt[i+1][j+1] = (i, j, str1[i])
+        
+        i, j = len(str1), len(str2)
+        result = []
+        while i != 0 or j != 0:
+            i, j, c = bt[i][j]
+            result.append(c)
+        result.reverse()
+        return "".join(result)