Question

我只需要一个基本的简单功能就可以了。

这是我的尝试：

function parseEq($eq) {
    $char = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']; 
    $achar = array_map('ord', $char);

    $eq = str_replace($char, $achar, $eq);

    return eval(strtr('return {eq};', [
        '{eq}' => strtr($eq, [
            '=' => '==',
        ])
    ]));
}

但这只适用于一些例子：

var_dump(parseEq('2x = 2x'));
var_dump(parseEq('a + b = b + a'));
var_dump(parseEq('x - x = 0'));
var_dump(parseEq('y/2 = (1/2)*y'));
var_dump(parseEq('-(-x) = x'));

但不适用于这两个

var_dump(parseEq('2(x + y) = 2x + 2y'));
var_dump(parseEq('2x = 2*x'));

Answer 1

<?php
function parseEq($eq) {
        $char = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'];
        $achar = array_map('ord', $char);

        // debug
        echo $eq . PHP_EOL;

        $eq = str_replace($char, $achar, $eq);

        // debug
        echo $eq . PHP_EOL;

        return eval(strtr('return {eq};', [
                '{eq}' => strtr($eq, [
                        '=' => '==',
                ])
        ]));
}

将产生

2x = 2x
2120 = 2120
bool(true)
a + b = b + a
97 + 98 = 98 + 97
bool(true)
x - x = 0
120 - 120 = 0
bool(true)
y/2 = (1/2)*y
121/2 = (1/2)*121
bool(true)
-(-x) = x
-(-120) = 120
bool(true)
2(x + y) = 2x + 2y
2(120 + 121) = 2120 + 2121
PHP Parse error:  syntax error, unexpected '(' in parseEq.php(16) : eval()'d code on line 1
bool(false)
2x = 2*x
2120 = 2*120
bool(false)

所以它试图将每个字母替换为普通值，如x到120.

经过少量修改

<?php
function parseEq($eq) {
    $char = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'];
    $achar = array_map('ord', $char);

    echo $eq . PHP_EOL;

    // replaceing 2( or 2x with 2* or 2*x
    $eq = preg_replace('/(\d+)([\(a-z])/', "$1*$2", $eq);
    echo $eq . PHP_EOL;

    $eq = str_replace($char, $achar, $eq);

    echo $eq . PHP_EOL;

    return eval(strtr('return {eq};', [
        '{eq}' => strtr($eq, [
            '=' => '==',
        ])
    ]));
}

它会产生

    2x = 2x
    2*x = 2*x
    2*120 = 2*120
    bool(true)
    a + b = b + a
    a + b = b + a
    97 + 98 = 98 + 97
    bool(true)
    x - x = 0
    x - x = 0
    120 - 120 = 0
    bool(true)
    y/2 = (1/2)*y
    y/2 = (1/2)*y
    121/2 = (1/2)*121
    bool(true)
    -(-x) = x
    -(-x) = x
    -(-120) = 120
    bool(true)
    2(x + y) = 2x + 2y
    2*(x + y) = 2*x + 2*y
    2*(120 + 121) = 2*120 + 2*121
    bool(true)
    2x = 2*x
    2*x = 2*x
    2*120 = 2*120
    bool(true)

所以它现在正在运作

如何在PHP中评估数学方程（BODMAS）？

1 个答案: