秒杀24点！用Python轻松计算并获取表达式

最编程 2024-02-01 11:55:54

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from operator import add, mul, sub, truediv
from itertools import permutations, combinations_with_replacement
from collections import defaultdict

def judgePoint24(nums) -> bool:
ops = [add, mul, sub, truediv]
op_char = "+*-/"
record = []

def solve(nums) -> bool:
if not nums:
return False
n = len(nums)
if n == 1:
return round(nums[0], 3) == 24
for i, j in permutations(range(n), 2):
# 选2个数字
x, y = nums[i], nums[j]
newNums = []
# 选择加减乘除 4 种运算操作之一，用得到的结果取代选出的 2 个数字
# 先添加未选择的数字
newNums = [z for k, z in enumerate(nums) if k not in (i, j)]
for k in range(4):
if k < 2 and i > j:
# 加法和乘法满足交换律,跳过第二种顺序
continue
if k == 3 and (round(y, 3) == 0):
# 除法运算除数不能为0
continue
v = ops[k](x, y)
newNums.append(v)
record.append(([round(x, 3), round(y, 3)],
op_char[k], round(v, 3)))
if solve(newNums):
return True
newNums.pop()
record.pop()
return False
flag = solve(nums)
if not flag:
return False, ""
cache = defaultdict(list)
for ns, op, v in record:
for i in range(2):
if cache[ns[i]]:
ns[i] = "("+cache[ns[i]].pop()+")"
a, b = ns
cache[v].append(f"{a}{op}{b}")
return flag, cache[24][0]+"=24"

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