Leetcode heroes

class Solution: def kSimilarity(self, a: str, b: str) -> int: return(f:=cache(lambda b:b and((x:=a[-len(b)])!=b[0]and 1+min(f(b[1:j]+b[0]+b[j+1:])for j,c in enumerate(b)if c==x)or f(b[1:]))or 0))(b)