Strings A and B are K-similar (for some non-negative integer K) if we can swap the positions of two letters in A exactly K times so that the resulting string equals B.
Given two anagrams A and B, return the smallest K for which A and B are K-similar.
Example 1:
Input: A = "ab", B = "ba"
Output: 1


Example 2:
Input: A = "abc", B = "bca"
Output: 2


Example 3:
Input: A = "abac", B = "baca"
Output: 2


Example 4:
Input: A = "aabc", B = "abca"
Output: 2



Note:

1 <= A.length == B.length <= 20
A and B contain only lowercase letters from the set {'a', 'b', 'c', 'd', 'e', 'f'}

```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 kSimilarity(self, A: str, B: str) -> int:\n#         n = len(A)\n#         A, B = list(A), list(B)\n#         mp = defaultdict(list)\n#         for i, ch in enumerate(A):\n#             mp[ch].append(i)\n#         def dfs(idx):\n#             if idx == n:\n#                 return 0\n#             if A[idx] == B[idx]:\n#                 return dfs(idx+1)\n#             res = float('inf')\n#             for nxt in range(idx+1,n):\n#                 if A[nxt] != B[idx]:\n#                     continue\n#                 A[idx], A[nxt] = A[nxt], A[idx]\n#                 res = min(res, dfs(idx+1)+1)\n#                 A[idx], A[nxt] = A[nxt], A[idx]\n#             return res\n#         return dfs(0)\n\nfrom functools import lru_cache\nclass Solution:\n    def kSimilarity(self, A: str, B: str) -> int:\n        n = len(A)\n        # mp = defaultdict(list)\n        # for i, ch in enumerate(A):\n        #     mp[ch].append(i)\n        @lru_cache(None)\n        def dfs(s):\n            if s == B:\n                return 0\n            idx = 0\n            while s[idx] == B[idx]:\n                idx += 1\n            res = float('inf')\n            for nxt in range(idx+1,n):\n                if s[nxt] != B[idx]:\n                # if s[nxt] != B[idx] or s[nxt] == B[nxt]:\n                    continue\n                res = min(res, dfs(s[:idx]+s[nxt]+s[idx+1:nxt]+s[idx]+s[nxt+1:])+1)\n            return res\n        return dfs(A)"
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'kSimilarity'
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: 8049