human
Solve in Python:
Given two strings str1 and str2, return the shortest string that has both str1 and str2 as subsequences.  If multiple answers exist, you may return any of them.
(A string S is a subsequence of string T if deleting some number of characters from T (possibly 0, and the characters are chosen anywhere from T) results in the string S.)
 
Example 1:
Input: str1 = "abac", str2 = "cab"
Output: "cabac"
Explanation: 
str1 = "abac" is a subsequence of "cabac" because we can delete the first "c".
str2 = "cab" is a subsequence of "cabac" because we can delete the last "ac".
The answer provided is the shortest such string that satisfies these properties.

 
Note:

1 <= str1.length, str2.length <= 1000
str1 and str2 consist of lowercase English letters.
assistant
#Here is the Python program you requested.

class Solution:
    def shortestCommonSupersequence(self, s1: str, s2: str) -> str:
        m, n = len(s1), len(s2)
        dp = [[''] * n for _ in range(m)]
        for i in range(m):
            for j in range(n):
                if s1[i] == s2[j]:
                    dp[i][j] = dp[i-1][j-1] + s1[i] if i > 0 and j > 0 else s1[i]
                else:
                    if i > 0 and j > 0:
                        dp[i][j] = max(dp[i-1][j], dp[i][j-1], key=lambda x:len(x))
                    elif i > 0:
                        dp[i][j] = dp[i-1][j]
                    elif j > 0:
                        dp[i][j] = dp[i][j-1]
        res, i, j = '', 0, 0
        for ch in dp[-1][-1]:
            while s1[i] != ch:
                res += s1[i]
                i += 1
            while s2[j] != ch:
                res += s2[j]
                j += 1
            res, i, j = res + ch, i + 1, j + 1
        res += s1[i:] + s2[j:]
        return res