Plusmiinusjonotrekursio

def recur(n):
    memo = {}
    def rec(j, a,b):
        if j==0: return 1 if a==0 and b==0 else 0
        memoKey = (j,a,b)
        if memoKey in memo: return memo[memoKey]
        ret = 0
        if a>0:
            ret += rec(j-1, a-1, b+1)
        if a==0 and b>0:
            ret += sum(rec(j-1, k, b-1) for k in range(4))
        memo[memoKey] = ret
        return ret
    return sum(rec(n, a,b) for a in range(4) for b in range(n+1))