本来想用回溯法实现 算24点。题目都拟好了，就是《python 回溯法 子集树模板 系列 —— 7、24点》。无奈想了一天，没有头绪。只好改用暴力穷举法。
思路说明
根据四个数，三个运算符，构造三种中缀表达式，遍历，计算每一种可能
显然可能的形式不止三种。但是，其它的形式要么得不到24点，要么在加、乘意义下可以转化为这三种形式的表达式！
使用内置的eval函数计算中缀表达式，使得代码变得非常简洁！
完整代码
# 作者：hhh5460# 时间：2017年6月3日import itertoolsdef twentyfour(cards): '''史上最短计算24点代码''' for nums in itertools.permutations(cards): # 四个数 for ops in itertools.product('+-*/', repeat=3): # 三个运算符（可重复！） # 构造三种中缀表达式 (bsd) bds1 = '({0}{4}{1}){5}({2}{6}{3})'.format(*nums, *ops) # (a+b)*(c-d) bds2 = '(({0}{4}{1}){5}{2}){6}{3}'.format(*nums, *ops) # (a+b)*c-d bds3 = '{0}{4}({1}{5}({2}{6}{3}))'.format(*nums, *ops) # a/(b-(c/d)) for bds in [bds1, bds2, bds3]: # 遍历 try: if abs(eval(bds) - 24.0) < 1e-10: # eval函数 return bds except ZeroDivisionError: # 零除错误！ continue return 'Not found!'# 测试# 数据来源：http://www.cnblogs.com/grenet/archive/2013/02/28/2936965.htmlcards =[[1,1,1,8], [1,1,2,6], [1,1,2,7], [1,1,2,8], [1,1,2,9], [1,1,2,10], [1,1,3,4], [1,1,3,5], [1,1,3,6], [1,1,3,7], [1,1,3,8], [1,1,3,9], [1,1,3,10], [1,1,4,4], [1,1,4,5], [1,1,4,6], [1,1,4,7], [1,1,4,8], [1,1,4,9], [1,1,4,10], [1,1,5,5], [1,1,5,6], [1,1,5,7], [1,1,5,8], [1,1,6,6], [1,1,6,8], [1,1,6,9], [1,1,7,10], [1,1,8,8], [1,2,2,4], [1,2,2,5], [1,2,2,6], [1,2,2,7], [1,2,2,8], [1,2,2,9], [1,2,2,10], [1,2,3,3], [1,2,3,4], [1,2,3,5], [1,2,3,6], [1,2,3,7], [1,2,3,8], [1,2,3,9], [1,2,3,10], [1,2,4,4], [1,2,4,5], [1,2,4,6], [1,2,4,7], [1,2,4,8], [1,2,4,9], [1,2,4,10], [1,2,5,5], [1,2,5,6], [1,2,5,7], [1,2,5,8], [1,2,5,9], [1,2,5,10], [1,2,6,6], [1,2,6,7], [1,2,6,8], [1,2,6,9], [1,2,6,10], [1,2,7,7], [1,2,7,8], [1,2,7,9], [1,2,7,10], [1,2,8,8], [1,2,8,9], [1,2,8,10], [1,3,3,3], [1,3,3,4], [1,3,3,5], [1,3,3,6], [1,3,3,7], [1,3,3,8], [1,3,3,9], [1,3,3,10], [1,3,4,4], [1,3,4,5], [1,3,4,6], [1,3,4,7], [1,3,4,8], [1,3,4,9], [1,3,4,10], [1,3,5,6], [1,3,5,7], [1,3,5,8], [1,3,5,9], [1,3,5,10], [1,3,6,6], [1,3,6,7], [1,3,6,8], [1,3,6,9], [1,3,6,10], [1,3,7,7], [1,3,7,8], [1,3,7,9], [1,3,7,10], [1,3,8,8], [1,3,8,9], [1,3,8,10], [1,3,9,9], [1,3,9,10], [1,3,10,10], [1,4,4,4], [1,4,4,5], [1,4,4,6], [1,4,4,7], [1,4,4,8], [1,4,4,9], [1,4,4,10], [1,4,5,5], [1,4,5,6], [1,4,5,7], [1,4,5,8], [1,4,5,9], [1,4,5,10], [1,4,6,6], [1,4,6,7], [1,4,6,8], [1,4,6,9], [1,4,6,10], [1,4,7,7], [1,4,7,8], [1,4,7,9], [1,4,8,8], [1,4,8,9], [1,4,9,10], [1,4,10,10], [1,5,5,5], [1,5,5,6], [1,5,5,9], [1,5,5,10], [1,5,6,6], [1,5,6,7], [1,5,6,8], [1,5,6,9], [1,5,6,10], [1,5,7,8], [1,5,7,9], [1,5,7,10], [1,5,8,8], [1,5,8,9], [1,5,8,10], [1,5,9,9], [1,5,9,10], [1,5,10,10], [1,6,6,6], [1,6,6,8], [1,6,6,9], [1,6,6,10], [1,6,7,9], [1,6,7,10], [1,6,8,8], [1,6,8,9], [1,6,8,10], [1,6,9,9], [1,6,9,10], [1,7,7,9], [1,7,7,10], [1,7,8,8], [1,7,8,9], [1,7,8,10], [1,7,9,9], [1,7,9,10], [1,8,8,8], [1,8,8,9], [1,8,8,10], [2,2,2,3], [2,2,2,4], [2,2,2,5], [2,2,2,7], [2,2,2,8], [2,2,2,9], [2,2,2,10], [2,2,3,3], [2,2,3,4], [2,2,3,5], [2,2,3,6], [2,2,3,7], [2,2,3,8], [2,2,3,9], [2,2,3,10], [2,2,4,4], [2,2,4,5], [2,2,4,6], [2,2,4,7], [2,2,4,8], [2,2,4,9], [2,2,4,10], [2,2,5,5], [2,2,5,6], [2,2,5,7], [2,2,5,8], [2,2,5,9], [2,2,5,10], [2,2,6,6], [2,2,6,7], [2,2,6,8], [2,2,6,9], [2,2,6,10], [2,2,7,7], [2,2,7,8], [2,2,7,10], [2,2,8,8], [2,2,8,9], [2,2,8,10], [2,2,9,10], [2,2,10,10], [2,3,3,3], [2,3,3,5], [2,3,3,6], [2,3,3,7], [2,3,3,8], [2,3,3,9], [2,3,3,10], [2,3,4,4], [2,3,4,5], [2,3,4,6], [2,3,4,7], [2,3,4,8], [2,3,4,9], [2,3,4,10], [2,3,5,5], [2,3,5,6], [2,3,5,7], [2,3,5,8], [2,3,5,9], [2,3,5,10], [2,3,6,6], [2,3,6,7], [2,3,6,8], [2,3,6,9], [2,3,6,10], [2,3,7,7], [2,3,7,8], [2,3,7,9], [2,3,7,10], [2,3,8,8], [2,3,8,9], [2,3,8,10], [2,3,9,9], [2,3,9,10], [2,3,10,10], [2,4,4,4], [2,4,4,5], [2,4,4,6], [2,4,4,7], [2,4,4,8], [2,4,4,9], [2,4,4,10], [2,4,5,5], [2,4,5,6], [2,4,5,7], [2,4,5,8], [2,4,5,9], [2,4,5,10], [2,4,6,6], [2,4,6,7], [2,4,6,8], [2,4,6,9], [2,4,6,10], [2,4,7,7], [2,4,7,8], [2,4,7,9], [2,4,7,10], [2,4,8,8], [2,4,8,9], [2,4,8,10], [2,4,9,9], [2,4,9,10], [2,4,10,10], [2,5,5,7], [2,5,5,8], [2,5,5,9], [2,5,5,10], [2,5,6,6], [2,5,6,7], [2,5,6,8], [2,5,6,9], [2,5,6,10], [2,5,7,7], [2,5,7,8], [2,5,7,9], [2,5,7,10], [2,5,8,8], [2,5,8,9], [2,5,8,10], [2,5,9,10], [2,5,10,10], [2,6,6,6], [2,6,6,7], [2,6,6,8], [2,6,6,9], [2,6,6,10], [2,6,7,8], [2,6,7,9], [2,6,7,10], [2,6,8,8], [2,6,8,9], [2,6,8,10], [2,6,9,9], [2,6,9,10], [2,6,10,10], [2,7,7,8], [2,7,7,10], [2,7,8,8], [2,7,8,9], [2,7,9,10], [2,7,10,10], [2,8,8,8], [2,8,8,9], [2,8,8,10], [2,8,9,9], [2,8,9,10], [2,8,10,10], [2,9,10,10], [3,3,3,3], [3,3,3,4], [3,3,3,5], [3,3,3,6], [3,3,3,7], [3,3,3,8], [3,3,3,9], [3,3,3,10], [3,3,4,4], [3,3,4,5], [3,3,4,6], [3,3,4,7], [3,3,4,8], [3,3,4,9], [3,3,5,5], [3,3,5,6], [3,3,5,7], [3,3,5,9], [3,3,5,10], [3,3,6,6], [3,3,6,7], [3,3,6,8], [3,3,6,9], [3,3,6,10], [3,3,7,7], [3,3,7,8], [3,3,7,9], [3,3,8,8], [3,3,8,9], [3,3,8,10], [3,3,9,9], [3,3,9,10], [3,4,4,4], [3,4,4,5], [3,4,4,6], [3,4,4,7], [3,4,4,8], [3,4,4,9], [3,4,4,10], [3,4,5,5], [3,4,5,6], [3,4,5,7], [3,4,5,8], [3,4,5,9], [3,4,5,10], [3,4,6,6], [3,4,6,8], [3,4,6,9], [3,4,6,10], [3,4,7,7], [3,4,7,8], [3,4,7,9], [3,4,7,10], [3,4,8,9], [3,4,8,10], [3,4,9,9], [3,4,10,10], [3,5,5,6], [3,5,5,7], [3,5,5,8], [3,5,5,9], [3,5,6,6], [3,5,6,7], [3,5,6,8], [3,5,6,9], [3,5,6,10], [3,5,7,8], [3,5,7,9], [3,5,7,10], [3,5,8,8], [3,5,8,9], [3,5,9,9], [3,5,9,10], [3,5,10,10], [3,6,6,6], [3,6,6,7], [3,6,6,8], [3,6,6,9], [3,6,6,10], [3,6,7,7], [3,6,7,8], [3,6,7,9], [3,6,7,10], [3,6,8,8], [3,6,8,9], [3,6,8,10], [3,6,9,9], [3,6,9,10], [3,6,10,10], [3,7,7,7], [3,7,7,8], [3,7,7,9], [3,7,7,10], [3,7,8,8], [3,7,8,9], [3,7,9,9], [3,7,9,10], [3,7,10,10], [3,8,8,8], [3,8,8,9], [3,8,8,10], [3,8,9,9], [3,8,9,10], [3,8,10,10], [3,9,9,9], [3,9,9,10], [3,9,10,10], [4,4,4,4], [4,4,4,5], [4,4,4,6], [4,4,4,7], [4,4,4,8], [4,4,4,9], [4,4,4,10], [4,4,5,5], [4,4,5,6], [4,4,5,7], [4,4,5,8], [4,4,5,10], [4,4,6,8], [4,4,6,9], [4,4,6,10], [4,4,7,7], [4,4,7,8], [4,4,7,9], [4,4,7,10], [4,4,8,8], [4,4,8,9], [4,4,8,10], [4,4,10,10], [4,5,5,5], [4,5,5,6], [4,5,5,7], [4,5,5,8], [4,5,5,9], [4,5,5,10], [4,5,6,6], [4,5,6,7], [4,5,6,8], [4,5,6,9], [4,5,6,10], [4,5,7,7], [4,5,7,8], [4,5,7,9], [4,5,7,10], [4,5,8,8], [4,5,8,9], [4,5,8,10], [4,5,9,9], [4,5,9,10], [4,5,10,10], [4,6,6,6], [4,6,6,7], [4,6,6,8], [4,6,6,9], [4,6,6,10], [4,6,7,7], [4,6,7,8], [4,6,7,9], [4,6,7,10], [4,6,8,8], [4,6,8,9], [4,6,8,10], [4,6,9,9], [4,6,9,10], [4,6,10,10], [4,7,7,7], [4,7,7,8], [4,7,8,8], [4,7,8,9], [4,7,8,10], [4,7,9,9], [4,7,9,10], [4,7,10,10], [4,8,8,8], [4,8,8,9], [4,8,8,10], [4,8,9,9], [4,8,9,10], [4,8,10,10], [4,9,9,10], [5,5,5,5], [5,5,5,6], [5,5,5,9], [5,5,6,6], [5,5,6,7], [5,5,6,8], [5,5,7,7], [5,5,7,8], [5,5,7,10], [5,5,8,8], [5,5,8,9], [5,5,8,10], [5,5,9,9], [5,5,9,10], [5,5,10,10], [5,6,6,6], [5,6,6,7], [5,6,6,8], [5,6,6,9], [5,6,6,10], [5,6,7,7], [5,6,7,8], [5,6,7,9], [5,6,8,8], [5,6,8,9], [5,6,8,10], [5,6,9,9], [5,6,9,10], [5,6,10,10], [5,7,7,9], [5,7,7,10], [5,7,8,8], [5,7,8,9], [5,7,8,10], [5,7,9,10], [5,7,10,10], [5,8,8,8], [5,8,8,9], [5,8,8,10], [5,9,10,10], [6,6,6,6], [6,6,6,8], [6,6,6,9], [6,6,6,10], [6,6,7,9], [6,6,7,10], [6,6,8,8], [6,6,8,9], [6,6,8,10], [6,6,9,10], [6,7,7,10], [6,7,8,9], [6,7,8,10], [6,7,9,9], [6,7,10,10], [6,8,8,8], [6,8,8,9], [6,8,8,10], [6,8,9,9], [6,8,9,10], [6,9,9,10], [6,10,10,10], [7,7,9,10], [7,8,8,9], [7,8,8,10], [7,8,9,10], [7,8,10,10], [8,8,8,10]]for card in cards: print(twentyfour(card))