就是这个样的粗爆，手搓一个计算器：排列计算器

线上运行，可以直接打开：排列计算器（在线计算器）

       作为程序员，没有合适的工具，就得手搓一个，PC端，移动端均可适用。废话不多说，直接上代码。

HTML:

<div class="calculator"><div class="form-group"><label for="n">n (总数):</label> <input id="n" min="0" type="number" placeholder="例如: 5"></div><div class="form-group"><label for="r">r (选取数):</label> <input id="r" min="0" type="number" placeholder="例如: 3"></div><button onclick="calculatePermutation()">计算排列</button><div id="result" class="result"></div></div>

JS:

function factorial(num) {
            if (num === 0 || num === 1) return 1;
            let result = 1;
            for (let i = 2; i <= num; i++) {
                result *= i;
            }
            return result;
        }

        function calculatePermutation() {
            const nInput = document.getElementById('n');
            const rInput = document.getElementById('r');
            const resultDiv = document.getElementById('result');

            const n = parseInt(nInput.value);
            const r = parseInt(rInput.value);

            if (isNaN(n) || isNaN(r) || n < 0 || r < 0 || r > n) {
                resultDiv.textContent = "请输入有效的 n 和 r 值，且满足 r ≤ n！";
                return;
            }

            // 计算排列 P(n, r) = n! / (n-r)!
            const permutation = factorial(n) / factorial(n - r);

            resultDiv.textContent = `排列结果: P(${n}, ${r}) = ${permutation.toLocaleString()}`;

        }

 CSS:

.calculator {
width: 100%;
    background-color: #333;
    color: white;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.3);
}


label {
    display: block;
    margin-bottom: 10px;
    font-size: 16px;
}

input, select {
    width: 100%!important;
    padding: 10px!important;
    margin-bottom: 20px;
       color: #000000; 
    border-radius: 5px;
    border: 1px solid #555;
    font-size: 16px!important;
    background-color: #ffffff!important;
}

button {
    width: 100%;
    padding: 10px;
    background-color: #007bff;
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-size: 16px;
        display: block;
        margin: 0px;
     margin-bottom: 20px;
    margin-left: 0px!important;
}

button:hover {
    background-color: orange;
}

.result {
    margin-top: 20px;
    text-align: center;
}

option {
        background-color: #ffffff;
}


p {
    font-size: 18px;
        margin-top: 5px!important;
}