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📜  谷歌表格参考单元格静态 - TypeScript (1)

📅  最后修改于: 2023-12-03 15:41:49.081000             🧑  作者: Mango

谷歌表格参考单元格静态 - TypeScript

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。

实现过程

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:

  1. 将表达式转换为 RPN。这可以使用 Shunting Yard 算法来完成,该算法使用两个栈来完成转换。在转换时,我们需要考虑运算符的优先级和结合顺序。
  2. 使用栈来计算 RPN 表达式的值。在计算时,我们从左到右依次扫描 RPN 表达式,如果遇到一个操作数,则将其推入栈中。如果遇到一个运算符,则从栈中弹出两个操作数,并使用该运算符对它们进行计算,然后将计算结果推回到栈中。

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。

总结

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。