📅  最后修改于: 2023-12-03 15:41:49.081000             🧑  作者: Mango
在谷歌表格中,参考单元格是指通过引用另一个单元格的值来计算当前单元格的值。在这里介绍如何使用 TypeScript 实现参考单元格的静态计算。
首先,我们需要定义一个函数 evaluate
,该函数用来计算参考单元格的值。该函数的输入参数为一个字符串,表示需要计算的表达式。然后,我们需要将该表达式转换为 RPN(逆波兰式),然后使用栈来计算。具体步骤如下:
以下是 TypeScript 的代码实现:
enum TokenType {
Number,
Operator,
LeftParen,
RightParen
}
class Token {
constructor(public type: TokenType, public value: string) { }
}
class Lexer {
private input: string;
private position: number = 0;
constructor(input: string) {
this.input = input;
}
public getNextToken(): Token | null {
if (this.position >= this.input.length) {
return null;
}
const char = this.input[this.position];
if (/\d/.test(char)) {
return this.readNumber();
}
if (/\+|\-|\*|\//.test(char)) {
return this.readOperator();
}
if (char === '(') {
this.position++;
return new Token(TokenType.LeftParen, '(');
}
if (char === ')') {
this.position++;
return new Token(TokenType.RightParen, ')');
}
throw new Error('Invalid character: ' + char);
}
private readNumber(): Token {
let value = '';
while (/\d/.test(this.input[this.position])) {
value += this.input[this.position];
this.position++;
}
return new Token(TokenType.Number, value);
}
private readOperator(): Token {
const value = this.input[this.position];
this.position++;
return new Token(TokenType.Operator, value);
}
}
class Parser {
private lexer: Lexer;
private currentToken: Token | null = null;
constructor(expression: string) {
this.lexer = new Lexer(expression);
}
public parse(): Token[] {
this.nextToken();
const output: Token[] = [];
const operators: Token[] = [];
while (this.currentToken != null) {
if (this.currentToken.type === TokenType.Number) {
output.push(this.currentToken);
} else if (this.currentToken.type === TokenType.Operator) {
while (operators.length > 0 && this.shouldPop(operators[operators.length - 1], this.currentToken)) {
output.push(operators.pop()!);
}
operators.push(this.currentToken);
} else if (this.currentToken.type === TokenType.LeftParen) {
operators.push(this.currentToken);
} else if (this.currentToken.type === TokenType.RightParen) {
while (operators.length > 0 && operators[operators.length - 1].type !== TokenType.LeftParen) {
output.push(operators.pop()!);
}
if (operators.length === 0) {
throw new Error('Mismatched parentheses');
}
operators.pop();
} else {
throw new Error('Invalid token');
}
this.nextToken();
}
while (operators.length > 0) {
if (operators[operators.length - 1].type === TokenType.LeftParen || operators[operators.length - 1].type === TokenType.RightParen) {
throw new Error('Mismatched parentheses');
}
output.push(operators.pop()!);
}
return output;
}
private shouldPop(left: Token, right: Token): boolean {
if (left.type === TokenType.LeftParen || right.type === TokenType.LeftParen) {
return false;
}
if (left.type === TokenType.RightParen) {
throw new Error('Mismatched parentheses');
}
const leftPrecedence = this.getPrecedence(left);
const rightPrecedence = this.getPrecedence(right);
if (leftPrecedence > rightPrecedence) {
return true;
}
if (leftPrecedence === rightPrecedence && left.type === TokenType.Operator && right.type === TokenType.Operator && (left.value === '*' || left.value === '/')) {
return true;
}
return false;
}
private getPrecedence(token: Token): number {
switch (token.value) {
case '+':
case '-':
return 1;
case '*':
case '/':
return 2;
}
return 0;
}
private nextToken() {
this.currentToken = this.lexer.getNextToken();
}
}
class Calculator {
private stack: number[] = [];
public evaluate(expression: string): number {
const parser = new Parser(expression);
const tokens = parser.parse();
for (const token of tokens) {
if (token.type === TokenType.Number) {
this.stack.push(parseFloat(token.value));
} else if (token.type === TokenType.Operator) {
const rightOperand = this.stack.pop();
const leftOperand = this.stack.pop();
if (leftOperand == null || rightOperand == null) {
throw new Error('Invalid expression');
}
switch (token.value) {
case '+':
this.stack.push(leftOperand + rightOperand);
break;
case '-':
this.stack.push(leftOperand - rightOperand);
break;
case '*':
this.stack.push(leftOperand * rightOperand);
break;
case '/':
if (rightOperand === 0) {
throw new Error('Division by zero');
}
this.stack.push(leftOperand / rightOperand);
break;
}
}
}
if (this.stack.length !== 1) {
throw new Error('Invalid expression');
}
return this.stack.pop()!;
}
}
console.log(new Calculator().evaluate('1+2*(3+4)-5/2')); // 10.5
以上代码实现了 Shunting Yard 算法、RPN 的计算以及栈的使用。
本文介绍了如何使用 TypeScript 实现谷歌表格中参考单元格的静态计算。这主要涉及到了 Shunting Yard 算法和栈的使用。在实现时,我们需要充分考虑运算符的优先级和结合顺序。