题解 | 24点游戏算法

import sys
def isok(lst,n):
    if len(lst) == 1:
        return round(lst[0],5) == round(n,5) or -round(lst[0],5) == round(n,5)
    else:
        if round(n,5) == 0:
            return False
        for i in range(len(lst)):
            m = lst[0:i] + lst[i+1:]
            x = lst[i]
            if isok(m,n+x) or isok(m,n/x) or isok(m,n*x) or isok(m,n-x) or isok(m,x-n) or isok(m,x/n):
                return True
        if len(lst) == 4:
            for i in range(3):
                for j in range(i+1,4):
                    a = lst[i]
                    b = lst[j]
                    k,l = {0,1,2,3}-{i,j}
                    c = lst[k]
                    d = lst[l]
                    if abs((a+b)*(c+d)) == 24 or abs((a-b)*(c+d)) == 24 or abs((a+b)*(c-d)) == 24 or abs((a-b)*(c-d)) == 24:
                        return True

        return False
while True:
    try:
        lst = list(map(int,input().split()))
        if isok(lst,24):
            print('true')
        else:
            print('false')
    except:
        break