diff --git a/gcd.html b/gcd.html
new file mode 100644
index 0000000..43f8f40
--- /dev/null
+++ b/gcd.html
@@ -0,0 +1,521 @@
+<!DOCTYPE html>
+<html lang="zh-CN">
+<head>
+<meta charset="UTF-8">
+<meta name="viewport" content="width=device-width, initial-scale=1.0">
+<title>欧几里得算法图解</title>
+<style>
+  * { box-sizing: border-box; }
+  body {
+    margin: 0;
+    font-family: 'Segoe UI', 'PingFang SC', 'Microsoft YaHei', sans-serif;
+    background: #f0f4f8;
+    display: flex;
+    justify-content: center;
+    align-items: center;
+    min-height: 100vh;
+    padding: 20px;
+  }
+  .container {
+    max-width: 900px;
+    width: 100%;
+    background: #fff;
+    border-radius: 16px;
+    padding: 28px 30px 20px;
+    box-shadow: 0 8px 30px rgba(0,0,0,.08);
+  }
+  h1 {
+    text-align: center;
+    margin: 0 0 4px;
+    color: #2c3e50;
+  }
+  .subtitle {
+    text-align: center;
+    color: #7f8c8d;
+    margin: 0 0 18px;
+    font-size: 16px;
+  }
+  code {
+    background: #ecf0f1;
+    padding: 2px 8px;
+    border-radius: 4px;
+    font-family: 'Cascadia Mono', Consolas, monospace;
+  }
+  .controls {
+    display: flex;
+    flex-wrap: wrap;
+    gap: 12px;
+    justify-content: center;
+    align-items: center;
+    margin-bottom: 10px;
+  }
+  .controls label {
+    font-size: 16px;
+    color: #2c3e50;
+  }
+  .controls input {
+    width: 90px;
+    padding: 7px 10px;
+    font-size: 16px;
+    border: 2px solid #dce1e6;
+    border-radius: 8px;
+    text-align: center;
+    transition: border-color .2s;
+  }
+  .controls input:focus {
+    outline: none;
+    border-color: #3498db;
+  }
+  button {
+    padding: 8px 18px;
+    border: none;
+    border-radius: 8px;
+    background: #3498db;
+    color: #fff;
+    font-size: 14px;
+    cursor: pointer;
+    transition: background .2s, opacity .2s;
+  }
+  button:hover {
+    background: #2980b9;
+  }
+  button.secondary {
+    background: #95a5a6;
+  }
+  button.secondary:hover {
+    background: #7f8c8d;
+  }
+  button:disabled {
+    opacity: .5;
+    cursor: not-allowed;
+  }
+  .sub-nav {
+    display: flex;
+    gap: 12px;
+    justify-content: center;
+    margin: 0 0 8px;
+  }
+  .legend {
+    display: flex;
+    flex-wrap: wrap;
+    gap: 18px;
+    justify-content: center;
+    margin: 8px 0 4px;
+    font-size: 14px;
+    color: #34495e;
+  }
+  .legend span {
+    display: inline-flex;
+    align-items: center;
+    gap: 6px;
+  }
+  .swatch {
+    display: inline-block;
+    width: 18px;
+    height: 18px;
+    border-radius: 4px;
+    border: 1px solid rgba(0,0,0,.15);
+  }
+  .info {
+    text-align: center;
+    min-height: 24px;
+    font-size: 16px;
+    color: #34495e;
+    margin: 10px 0 4px;
+  }
+  .equation {
+    text-align: center;
+    font-size: 24px;
+    font-family: 'Cascadia Mono', Consolas, monospace;
+    color: #c0392b;
+    margin: 6px 0 10px;
+  }
+  .eq-note {
+    font-size: 14px;
+    color: #7f8c8d;
+  }
+  .canvas-wrap {
+    text-align: center;
+  }
+  canvas {
+    max-width: 100%;
+    height: auto;
+    border: 1px solid #e8ecf0;
+    border-radius: 12px;
+    background: #fbfcfd;
+  }
+  .note {
+    text-align: center;
+    color: #95a5a6;
+    font-size: 13px;
+    margin-top: 8px;
+  }
+  .result {
+    text-align: center;
+    font-size: 22px;
+    color: #27ae60;
+    margin: 12px 0 6px;
+    font-weight: bold;
+  }
+  .steps {
+    position: relative;
+    background: #fafbfc;
+    border: 1px solid #eef1f4;
+    border-radius: 10px;
+    padding: 10px 12px;
+    margin-top: 14px;
+    max-height: 220px;
+    overflow-y: auto;
+    font-size: 15px;
+    line-height: 1.7;
+  }
+  .step {
+    padding: 5px 10px;
+    border-left: 4px solid #dfe6ea;
+    border-radius: 0 6px 6px 0;
+    margin: 5px 0;
+    background: #fff;
+  }
+  .step.active {
+    background: #eef6fd;
+    border-left-color: #3498db;
+  }
+  .step.swap {
+    color: #7f8c8d;
+    border-left-color: #f39c12;
+    background: #fef9f2;
+  }
+  .step-eq {
+    color: #7f8c8d;
+    font-family: monospace;
+    font-size: 13px;
+    margin-left: 12px;
+  }
+</style>
+</head>
+<body>
+
+<div class="container">
+  <h1>欧几里得算法图解</h1>
+  <p class="subtitle">核心公式：<code>gcd(a, b) = gcd(b, a mod b)</code></p>
+
+  <div class="controls">
+    <label>a = <input id="num1" type="number" min="1" step="1" value="24"></label>
+    <label>b = <input id="num2" type="number" min="1" step="1" value="18"></label>
+    <button onclick="start()">开始演示</button>
+    <button id="autoBtn" class="secondary" onclick="toggleAuto()">自动演示</button>
+    <button class="secondary" onclick="randomExample()">随机示例</button>
+  </div>
+
+  <div class="sub-nav">
+    <button id="prevBtn" onclick="prev()">◀ 上一步</button>
+    <button id="nextBtn" onclick="next()">下一步 ▶</button>
+  </div>
+
+  <div class="legend">
+    <span><span class="swatch" style="background:rgba(52,152,219,.6);"></span> 边长为当前较小数的正方形，共 q 个</span>
+    <span><span class="swatch" style="background:rgba(243,156,18,.75);"></span> 余数带，旋转后成为下一步的矩形</span>
+  </div>
+
+  <div id="info" class="info"></div>
+  <div id="equation" class="equation"></div>
+  <div class="canvas-wrap">
+    <canvas id="canvas" width="760" height="460"></canvas>
+  </div>
+
+  <div class="note">示意图按同一比例缩放；橙色余数条旋转 90° 后就是下一步要切的矩形。</div>
+  <div id="result" class="result" style="display:none;"></div>
+
+  <div id="steps" class="steps"></div>
+</div>
+
+<script>
+  const canvas = document.getElementById('canvas');
+  const ctx = canvas.getContext('2d');
+
+  let steps = [];
+  let current = 0;
+  let timer = null;
+  let originalA = 0;
+  let originalB = 0;
+
+  // 生成欧几里得算法的每一步
+  function computeSteps(a, b) {
+    let m = Math.max(a, b);
+    let n = Math.min(a, b);
+    const arr = [];
+    while (n > 0) {
+      const q = Math.floor(m / n);
+      const r = m % n;
+      arr.push({ m, n, q, r });
+      m = n;
+      n = r;
+    }
+    return arr;
+  }
+
+  function stopAuto() {
+    if (timer) {
+      clearInterval(timer);
+      timer = null;
+      document.getElementById('autoBtn').textContent = '自动演示';
+    }
+  }
+
+  function start() {
+    const a = parseInt(document.getElementById('num1').value, 10);
+    const b = parseInt(document.getElementById('num2').value, 10);
+    if (!Number.isInteger(a) || !Number.isInteger(b) || a <= 0 || b <= 0) {
+      alert('请输入正整数！');
+      return;
+    }
+    originalA = a;
+    originalB = b;
+    steps = computeSteps(a, b);
+    current = 0;
+    stopAuto();
+    update();
+  }
+
+  function next() {
+    stopAuto();
+    if (current < steps.length - 1) {
+      current++;
+      update();
+    }
+  }
+
+  function prev() {
+    stopAuto();
+    if (current > 0) {
+      current--;
+      update();
+    }
+  }
+
+  function toggleAuto() {
+    if (timer) {
+      stopAuto();
+      return;
+    }
+    if (steps.length === 0) start();
+    if (steps.length === 0) return;
+
+    if (current >= steps.length - 1) {
+      current = 0;
+      update();
+    }
+
+    document.getElementById('autoBtn').textContent = '暂停';
+    timer = setInterval(() => {
+      if (current < steps.length - 1) {
+        current++;
+        update();
+      } else {
+        stopAuto();
+      }
+    }, 2000);
+  }
+
+  function update() {
+    if (steps.length === 0) return;
+
+    const step = steps[current];
+    const total = steps.length;
+
+    drawStep(step);
+
+    const info = document.getElementById('info');
+    const equation = document.getElementById('equation');
+    const result = document.getElementById('result');
+
+    if (step.r === 0) {
+      info.innerHTML = `第 ${current + 1} / ${total} 步：余数为 0，图中已经全是边长为 <b>${step.n}</b> 的正方形。`;
+      equation.innerHTML = `gcd(${step.m}, ${step.n}) = <b>${step.n}</b> <span class="eq-note">(${step.m} = ${step.q} × ${step.n} + 0)</span>`;
+      result.innerHTML = `✅ gcd(${originalA}, ${originalB}) = <b>${step.n}</b>`;
+      result.style.display = 'block';
+    } else {
+      info.innerHTML = `第 ${current + 1} / ${total} 步：从 ${step.m} × ${step.n} 的矩形中，最多切出 <b>${step.q}</b> 个边长为 <b>${step.n}</b> 的正方形，剩余 <b>${step.r}</b> × ${step.n} 的橙色余条。`;
+      equation.innerHTML = `gcd(${step.m}, ${step.n}) = gcd(${step.n}, ${step.r}) <span class="eq-note">(${step.m} = ${step.q} × ${step.n} + ${step.r})</span>`;
+      result.style.display = 'none';
+    }
+
+    document.getElementById('prevBtn').disabled = (current === 0);
+    document.getElementById('nextBtn').disabled = (current === total - 1);
+
+    renderSteps();
+  }
+
+  function renderSteps() {
+    const stepsDiv = document.getElementById('steps');
+    let html = '';
+
+    // 如果输入时 a < b，为了画成“较宽矩形”，先交换说明
+    if (originalA && originalB && originalA !== originalB && originalA < originalB) {
+      html += `<div class="step swap">交换：gcd(${originalA}, ${originalB}) = gcd(${originalB}, ${originalA})（方便画图）</div>`;
+    }
+
+    steps.forEach((s, i) => {
+      const cls = 'step' + (i === current ? ' active' : '');
+      if (s.r === 0) {
+        html += `<div class="${cls}"><b>第${i + 1}步</b>：gcd(${s.m}, ${s.n}) = ${s.n}<span class="step-eq">${s.m} = ${s.q} × ${s.n} + 0</span></div>`;
+      } else {
+        html += `<div class="${cls}"><b>第${i + 1}步</b>：gcd(${s.m}, ${s.n}) = gcd(${s.n}, ${s.r})<span class="step-eq">${s.m} = ${s.q} × ${s.n} + ${s.r}</span></div>`;
+      }
+    });
+
+    stepsDiv.innerHTML = html;
+
+    const active = stepsDiv.querySelector('.active');
+    if (active) {
+      const top = active.offsetTop;
+      const bottom = top + active.offsetHeight;
+      if (top < stepsDiv.scrollTop || bottom > stepsDiv.scrollTop + stepsDiv.clientHeight) {
+        stepsDiv.scrollTop = top - (stepsDiv.clientHeight - active.offsetHeight) / 2;
+      }
+    }
+  }
+
+  // 绘制当前步骤的矩形图解
+  function drawStep(step) {
+    const { m, n, q, r } = step;
+    const W = canvas.width;
+    const H = canvas.height;
+
+    ctx.clearRect(0, 0, W, H);
+
+    const left = 70, right = 50, top = 20, bottom = 55;
+    const availW = W - left - right;
+    const availH = H - top - bottom;
+    const scale = Math.min(availW / m, availH / n);
+
+    const rectW = m * scale;
+    const rectH = n * scale;
+    const x = (W - rectW) / 2;
+    const y = (H - rectH) / 2;
+
+    ctx.save();
+
+    // 外矩形背景
+    ctx.fillStyle = '#f4f7f9';
+    ctx.strokeStyle = '#2c3e50';
+    ctx.lineWidth = 2;
+    ctx.fillRect(x, y, rectW, rectH);
+    ctx.strokeRect(x, y, rectW, rectH);
+
+    const squareSize = n * scale;
+    const maxDraw = 60;
+
+    // 绘制蓝色正方形
+    if (q <= maxDraw) {
+      ctx.fillStyle = 'rgba(52,152,219,0.6)';
+      ctx.strokeStyle = 'rgba(46,134,193,0.8)';
+      ctx.lineWidth = 1;
+      for (let i = 0; i < q; i++) {
+        ctx.fillRect(x + i * squareSize, y, squareSize, squareSize);
+        ctx.strokeRect(x + i * squareSize, y, squareSize, squareSize);
+      }
+    } else {
+      // 如果方块太多，只画两端的一部分，中间用文字表示
+      const leftCount = 15;
+      const rightCount = 15;
+
+      ctx.fillStyle = 'rgba(52,152,219,0.6)';
+      ctx.strokeStyle = 'rgba(46,134,193,0.8)';
+      ctx.lineWidth = 1;
+
+      for (let i = 0; i < leftCount; i++) {
+        ctx.fillRect(x + i * squareSize, y, squareSize, squareSize);
+        ctx.strokeRect(x + i * squareSize, y, squareSize, squareSize);
+      }
+      for (let i = q - rightCount; i < q; i++) {
+        ctx.fillRect(x + i * squareSize, y, squareSize, squareSize);
+        ctx.strokeRect(x + i * squareSize, y, squareSize, squareSize);
+      }
+
+      const midStart = x + leftCount * squareSize;
+      const midWidth = (q - leftCount - rightCount) * squareSize;
+      ctx.fillStyle = 'rgba(52,152,219,0.2)';
+      ctx.fillRect(midStart, y, midWidth, rectH);
+      ctx.fillStyle = '#2c3e50';
+      ctx.font = '14px sans-serif';
+      ctx.textAlign = 'center';
+      ctx.textBaseline = 'middle';
+      ctx.fillText(`共 ${q} 个`, x + (q / 2) * squareSize, y + rectH / 2);
+    }
+
+    // 绘制橙色余数带
+    if (r > 0) {
+      const rx = x + q * squareSize;
+      const rw = r * scale;
+
+      ctx.fillStyle = 'rgba(243,156,18,0.75)';
+      ctx.strokeStyle = 'rgba(230,126,34,0.9)';
+      ctx.lineWidth = 1.5;
+      ctx.fillRect(rx, y, rw, rectH);
+      ctx.strokeRect(rx, y, rw, rectH);
+
+      if (rw > 35 && rectH > 35) {
+        ctx.fillStyle = '#6e4a00';
+        ctx.font = 'bold 14px sans-serif';
+        ctx.textAlign = 'center';
+        ctx.textBaseline = 'middle';
+        ctx.fillText(`r=${r}`, rx + rw / 2, y + rectH / 2);
+      }
+    }
+
+    // 重新描边，让外框更清晰
+    ctx.strokeStyle = '#2c3e50';
+    ctx.lineWidth = 2;
+    ctx.strokeRect(x, y, rectW, rectH);
+
+    // 尺寸标注
+    ctx.fillStyle = '#2c3e50';
+    ctx.font = 'bold 15px sans-serif';
+    ctx.textAlign = 'center';
+    ctx.textBaseline = 'alphabetic';
+    ctx.fillText(`m = ${m}`, x + rectW / 2, y + rectH + 28);
+
+    ctx.save();
+    ctx.translate(x - 28, y + rectH / 2);
+    ctx.rotate(-Math.PI / 2);
+    ctx.textAlign = 'center';
+    ctx.textBaseline = 'middle';
+    ctx.fillText(`n = ${n}`, 0, 0);
+    ctx.restore();
+
+    ctx.restore();
+  }
+
+  // 随机示例
+  function randomExample() {
+    const examples = [
+      [1071, 462],
+      [24, 18],
+      [180, 48],
+      [98, 56],
+      [55, 34],
+      [240, 126],
+      [13, 7],
+      [625, 125],
+      [97, 13],
+      [31415, 27182],
+      [64, 36],
+      [119, 34]
+    ];
+    const [a, b] = examples[Math.floor(Math.random() * examples.length)];
+    document.getElementById('num1').value = a;
+    document.getElementById('num2').value = b;
+    start();
+  }
+
+  // 页面加载后默认演示 24 和 18
+  window.addEventListener('DOMContentLoaded', () => {
+    document.getElementById('num1').value = 24;
+    document.getElementById('num2').value = 18;
+    start();
+  });
+</script>
+
+</body>
+</html>
\ No newline at end of file
