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.

```python

USER_FILENAME = "<user_code>"
import sys, json, builtins
import math, heapq, bisect, itertools, functools, collections, statistics, fractions, decimal, operator, array, random, re, string, os, pathlib
try:
    import resource as _res
except Exception:
    _res = None
from collections import Counter, defaultdict, deque, OrderedDict
from functools import lru_cache, reduce
from itertools import accumulate, permutations, combinations, product
from math import gcd, ceil, floor, sqrt
from decimal import Decimal
try:
    from typing import *
except Exception:
    pass
try:
    sys.setrecursionlimit(1_000_000)
except Exception:
    pass
try:
    import site as _site
    try:
        _sys_sites = _site.getsitepackages() if hasattr(_site, "getsitepackages") else []
        for _p in _sys_sites:
            if _p and _p not in sys.path:
                sys.path.append(_p)
    except Exception:
        pass
    try:
        _usp = _site.getusersitepackages()
        if isinstance(_usp, str):
            _usp = [_usp]
        for _p in _usp:
            if _p and _p not in sys.path:
                sys.path.append(_p)
    except Exception:
        pass
except Exception:
    pass

def _disabled_input(*args, **kwargs):
    raise RuntimeError("input() is disabled in callable mode")
builtins.input = _disabled_input

ns = {"__name__": "__judge__"}  # prevent if __name__ == "__main__" blocks
for _k, _v in list(globals().items()):
    if not _k.startswith("_"):
        ns[_k] = _v
_CODE = "class Solution:\n    def shortestCommonSupersequence(self, str1: str, str2: str) -> str:\n        len_str1 = len(str1)\n        len_str2 = len(str2)\n        matrix = [[[0, ''] for x in range(len_str1)] for y in range(len_str2)]\n        for i in range(len_str2):\n            for k in range(len_str1):\n                if(i == 0 and k == 0):\n                    if(str1[0] == str2[0]):\n                        matrix[i][k] = [1, 'D']\n                elif(i == 0):\n                    if(str2[i] == str1[k]):\n                        matrix[i][k] = [1, 'D']\n                    else:\n                        matrix[i][k] = [matrix[i][k-1][0], 'L']\n                elif(k == 0):\n                    if(str2[i] == str1[k]):\n                        matrix[i][k] = [1, 'D']\n                    else:\n                        matrix[i][k] = [matrix[i-1][k][0], 'U']\n                else:\n                    if(str2[i] == str1[k]):\n                        matrix[i][k] = [matrix[i-1][k-1][0]+1, 'D']\n                    else:\n                        if(matrix[i][k-1][0] > matrix[i-1][k][0]):\n                            matrix[i][k] = [matrix[i][k-1][0], 'L']\n                        else:\n                            matrix[i][k] = [matrix[i-1][k][0], 'R']\n        if(matrix[-1][-1] == 0):\n            return str1+str2\n        str1_lis, str2_lis = [], []\n        str_val = ''\n        val = matrix[-1][-1][0]\n        i, k = len_str2-1, len_str1-1\n        while(val > 0):\n            if(matrix[i][k][1] == 'D'):\n                val -= 1\n                str_val += str2[i]\n                str1_lis.append(k)\n                str2_lis.append(i)\n                i -= 1\n                k -= 1\n            elif(matrix[i][k][1] == 'L'):\n                k -= 1\n            else:\n                i -= 1\n        #for i in matrix:\n        #    print(i)\n        str_val = str_val[::-1]\n        str1_lis = str1_lis[::-1]\n        str2_lis = str2_lis[::-1]\n        #print(str_val, str1_lis, str2_lis)\n        final_str = str1[:str1_lis[0]] + str2[:str2_lis[0]] + str_val[0]\n        for i in range(1, len(str_val)):\n            final_str += str1[str1_lis[i-1]+1:str1_lis[i]] + str2[str2_lis[i-1]+1:str2_lis[i]] + str_val[i]\n        if(str1_lis[-1] < len_str1-1):\n            final_str += str1[str1_lis[-1]+1:]\n        if(str2_lis[-1] < len_str2-1):\n            final_str += str2[str2_lis[-1]+1:]\n        return final_str"
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'shortestCommonSupersequence'
if _fn_name:
    if "Solution" in ns:
        try:
            _obj = ns["Solution"]()
            if hasattr(_obj, _fn_name):
                _target = getattr(_obj, _fn_name)
        except Exception:
            _target = None
    if _target is None and _fn_name in ns and callable(ns[_fn_name]):
        _target = ns[_fn_name]
# Fallback: if there's exactly one user-defined function, use it
if _target is None:
    _cands = [v for k, v in ns.items() if callable(v) and getattr(v, "__module__", "") in ("__judge__", "__main__")]
    _user_funcs = [c for c in _cands if getattr(c, "__name__", "").startswith("_") is False]
    if len(_user_funcs) == 1:
        _target = _user_funcs[0]
if _target is None:
    raise RuntimeError(f"Could not resolve callable '{_fn_name}'")

_raw = sys.stdin.read().strip()
if _raw:
    _parsed = json.loads(_raw)
    if isinstance(_parsed, dict):
        _kwargs = _parsed.get("kwargs", {})
        _args = _parsed.get("args", [])
    else:
        _args, _kwargs = _parsed, {}
else:
    _args, _kwargs = [], {}
if not isinstance(_args, (list, tuple)):
    _args = [_args]
_res = _target(*_args, **_kwargs)
try:
    sys.stdout.write(repr(_res) + "\n")
except Exception:
    pass

```

Measured memory_bytes: 10326