# Time: +: O(d * t), t is the number of terms, # d is the average degree of terms # -: O(d * t) # *: O(d * t^2) # eval: O(d * t) # to_list: O(d * tlogt) # Space: O(e + d * t), e is the number of evalvars # Given an expression such as expression = "e + 8 - a + 5" and # an evaluation map such as {"e": 1} # (given in terms of evalvars = ["e"] and evalints = [1]), # return a list of tokens representing the simplified expression, # such as ["-1*a","14"] # - An expression alternates chunks and symbols, # with a space separating each chunk and symbol. # - A chunk is either an expression in parentheses, a variable, # or a non-negative integer. # - A variable is a string of lowercase letters (not including digits.) # Note that variables can be multiple letters, and note that variables never # have a leading coefficient or unary operator like "2x" or "-x". # # Expressions are evaluated in the usual order: # brackets first, then multiplication, then addition and subtraction. # For example, expression = "1 + 2 * 3" has an answer of ["7"]. # # The format of the output is as follows: # - For each term of free variables with non-zero coefficient, # we write the free variables within a term in sorted order # lexicographically. # For example, we would never write a term like "b*a*c", only "a*b*c". # - Terms have degree equal to the number of free variables being multiplied, # counting multiplicity. (For example, "a*a*b*c" has degree 4.) # We write the largest degree terms of our answer first, # breaking ties by lexicographic order ignoring the leading coefficient of # the term. # - The leading coefficient of the term is placed directly to the left with an # asterisk separating it from the variables (if they exist.) # A leading coefficient of 1 is still printed. # - An example of a well formatted answer is # ["-2*a*a*a", "3*a*a*b", "3*b*b", "4*a", "5*c", "-6"] # - Terms (including constant terms) with coefficient 0 are not included. # For example, an expression of "0" has an output of []. # # Examples: # # Input: expression = "e + 8 - a + 5", evalvars = ["e"], evalints = [1] # Output: ["-1*a","14"] # # Input: expression = "e - 8 + temperature - pressure", # evalvars = ["e", "temperature"], evalints = [1, 12] # Output: ["-1*pressure","5"] # # Input: expression = "(e + 8) * (e - 8)", evalvars = [], evalints = [] # Output: ["1*e*e","-64"] # # Input: expression = "7 - 7", evalvars = [], evalints = [] # Output: [] # # Input: expression = "a * b * c + b * a * c * 4", evalvars = [], evalints = [] # Output: ["5*a*b*c"] # # Input: expression = # "((a - b) * (b - c) + (c - a)) * ((a - b) + (b - c) * (c - a))", # evalvars = [], evalints = [] # Output: # ["-1*a*a*b*b","2*a*a*b*c","-1*a*a*c*c","1*a*b*b*b","-1*a*b*b*c","-1*a*b*c*c", # "1*a*c*c*c","-1*b*b*b*c","2*b*b*c*c","-1*b*c*c*c","2*a*a*b","-2*a*a*c","-2*a*b*b", # "2*a*c*c","1*b*b*b","-1*b*b*c","1*b*c*c","-1*c*c*c","-1*a*a","1*a*b","1*a*c","-1*b*c"] # # Note: # - expression will have length in range [1, 1000]. # - evalvars, evalints will have equal lengths in range [0, 1000]. import collections import itertools try: xrange # Python 2 except NameError: xrange = range # Python 3 class Poly(collections.Counter): def __init__(self, expr=None): if expr is None: return if expr.isdigit(): self.update({(): int(expr)}) else: self[(expr,)] += 1 def __add__(self, other): self.update(other) return self def __sub__(self, other): self.update({k: -v for k, v in other.items()}) return self def __mul__(self, other): def merge(k1, k2): result = [] i, j = 0, 0 while i != len(k1) or j != len(k2): if j == len(k2): result.append(k1[i]) i += 1 elif i == len(k1): result.append(k2[j]) j += 1 elif k1[i] < k2[j]: result.append(k1[i]) i += 1 else: result.append(k2[j]) j += 1 return result result = Poly() for k1, v1 in self.items(): for k2, v2 in other.items(): result.update({tuple(merge(k1, k2)): v1*v2}) return result def eval(self, lookup): result = Poly() for polies, c in self.items(): key = [] for var in polies: if var in lookup: c *= lookup[var] else: key.append(var) result[tuple(key)] += c return result def to_list(self): return ["*".join((str(v),) + k) for k, v in sorted(self.items(), key=lambda x: (-len(x[0]), x[0])) if v] class Solution(object): def basicCalculatorIV(self, expression, evalvars, evalints): """ :type expression: str :type evalvars: List[str] :type evalints: List[int] :rtype: List[str] """ def compute(operands, operators): left, right = operands.pop(), operands.pop() op = operators.pop() if op == '+': operands.append(left + right) elif op == '-': operands.append(left - right) elif op == '*': operands.append(left * right) def parse(s): if not s: return Poly() operands, operators = [], [] operand = "" for i in reversed(xrange(len(s))): if s[i].isalnum(): operand += s[i] if i == 0 or not s[i-1].isalnum(): operands.append(Poly(operand[::-1])) operand = "" elif s[i] == ')' or s[i] == '*': operators.append(s[i]) elif s[i] == '+' or s[i] == '-': while operators and operators[-1] == '*': compute(operands, operators) operators.append(s[i]) elif s[i] == '(': while operators[-1] != ')': compute(operands, operators) operators.pop() while operators: compute(operands, operators) return operands[-1] lookup = dict(itertools.izip(evalvars, evalints)) return parse(expression).eval(lookup).to_list()