Master the fast algorithm and implementation method of converting Roman numerals to integers in PHP.

Master the fast algorithm and implementation method of converting Roman numerals to integers in PHP

In daily development, we often encounter the need to convert Roman numerals to integers. For example, convert the Roman numeral represented by "IV" to the integer 4. Although PHP provides a basic conversion function roman_numerals(), its performance is not high, especially when processing large amounts of data. This article will introduce a fast algorithm and the corresponding PHP implementation.

First, let’s take a look at the correspondence between Roman numerals and integers:

Roman numerals	corresponds to integers
I	1
IV	4
V	5
IX	9
X	10
XL	40
L	50
XC	90
C	100
CD	400
D	500
CM	900
M	1000

Observing this table, we can find that except for special cases (such as "I", "X", "C" on the left means subtraction), each character of Roman numerals is the accumulation of a corresponding integer. Therefore, we can traverse the Roman numeral string from left to right, compare the size relationship between the current character and the next character, and then decide whether to perform addition or subtraction.

The following is the specific implementation code:

function romanToInt($s) {
    $num = 0;
    $len = strlen($s);

    for ($i = 0; $i < $len; $i++) {
        // 获取当前字符的整数值
        $curNum = getValue($s[$i]);

        // 如果当前字符比下一个字符小，则进行减法操作
        if ($i < $len - 1 && $curNum < getValue($s[$i + 1])) {
            $num -= $curNum;
        } else {    // 否则进行加法操作
            $num += $curNum;
        }
    }

    return $num;
}

// 获取字符对应的整数值
function getValue($ch) {
    switch ($ch) {
        case 'I': return 1;
        case 'V': return 5;
        case 'X': return 10;
        case 'L': return 50;
        case 'C': return 100;
        case 'D': return 500;
        case 'M': return 1000;
        default: return 0;
    }
}

// 测试代码
echo romanToInt('IV');   // 输出 4

In the above code, we define a romanToInt() function to implement the conversion operation of Roman numerals to integers. When traversing the Roman numeral string, we obtain the integer value of the current character through the getValue() function, and then compare the value with the value of the next character to decide whether to perform addition or subtraction.

Through this algorithm, we can quickly and accurately convert Roman numerals into corresponding integers without relying on PHP's native conversion function, thereby improving code execution efficiency.

To summarize, this article introduces a fast algorithm and the corresponding PHP implementation to convert Roman numerals to integers. We can efficiently convert Roman numerals to integers by iterating through the Roman numeral string from left to right and adding or subtracting the current character. This algorithm performs well with large amounts of data and is suitable for various combinations of Roman numerals. I hope this article will be helpful to you in dealing with Roman numeral conversion problems in PHP development.

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