[Swift]LeetCode770. 基本计算器 IV | Basic Calculator IV

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:

1. expression will have length in range [1, 250].
2. evalvars, evalints will have equal lengths in range [0, 100].

• 表达式交替使用块和符号，每个块和符号之间有一个空格。
• 块要么是括号中的表达式，要么是变量，要么是非负整数。
• 块是括号中的表达式，变量或非负整数。
• 变量是一个由小写字母组成的字符串（不包括数字）。请注意，变量可以是多个字母，并注意变量从不具有像 "2x" 或 "-x" 这样的前导系数或一元运算符 。

表达式按通常顺序进行求值：先是括号，然后求乘法，再计算加法和减法。例如，expression = "1 + 2 * 3" 的答案是 ["7"]。

输出格式如下：

• 对于系数非零的每个自变量项，我们按字典排序的顺序将自变量写在一个项中。例如，我们永远不会写像 “b*a*c” 这样的项，只写 “a*b*c”。
• 项的次数等于被乘的自变量的数目，并计算重复项。(例如，"a*a*b*c" 的次数为 4。)。我们先写出答案的最大次数项，用字典顺序打破关系，此时忽略词的前导系数。
• 项的前导系数直接放在左边，用星号将它与变量分隔开(如果存在的话)。前导系数 1 仍然要打印出来。
• 格式良好的一个示例答案是 ["-2*a*a*a", "3*a*a*b", "3*b*b", "4*a", "5*c", "-6"] 。
• 系数为 0 的项（包括常数项）不包括在内。例如，“0” 的表达式输出为 []。

示例：

输入：expression = "e + 8 - a + 5", evalvars = ["e"], evalints = [1]
输出：["-1*a","14"]

输入：expression = "e - 8 + temperature - pressure",
evalvars = ["e", "temperature"], evalints = [1, 12]
输出：["-1*pressure","5"]

输入：expression = "(e + 8) * (e - 8)", evalvars = [], evalints = []
输出：["1*e*e","-64"]

输入：expression = "7 - 7", evalvars = [], evalints = []
输出：[]

输入：expression = "a * b * c + b * a * c * 4", evalvars = [], evalints = []
输出：["5*a*b*c"]

输入：expression = "((a - b) * (b - c) + (c - a)) * ((a - b) + (b - c) * (c - a))",
evalvars = [], evalints = []
输出：["-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"]

提示：

1. expression 的长度在 [1, 250] 范围内。
2. evalvars, evalints 在范围 [0, 100] 内，且长度相同。

原文地址：https://www.cnblogs.com/strengthen/p/10536324.html