{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# AP CSA Demo — 普林斯顿 algs4 库（JAVA）\n",
    "\n",
    "这是 MVP 示例：教你如何用 **jjava (Java kernel)** 加载普林斯顿 `algs4.jar`，实现 **科学绘图 (StdDraw)** 和 **音频 (StdAudio)**。\n",
    "\n",
    "> algs4.jar 官方地址：https://algs4.cs.princeton.edu/code/algs4.jar"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 第 1 步：加载 algs4.jar（每个 notebook 首格执行一次）"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "%classpath add /opt/tljh/user/share/java/algs4.jar\n",
    "\n",
    "import edu.princeton.cs.algs4.StdOut;\n",
    "import edu.princeton.cs.algs4.StdDraw;\n",
    "import edu.princeton.cs.algs4.StdAudio;\n",
    "\n",
    "StdOut.println(\"algs4 加载成功!\");"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 第 2 步：科学绘图 — StdDraw 画一个函数曲线\n",
    "\n",
    "服务器无显示器 (headless)，所以我们**离屏渲染后保存为 PNG**，再用 Markdown 显示。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "// 离屏绘图：sin 曲线\n",
    "int n = 100;\n",
    "StdDraw.setCanvasSize(600, 400);\n",
    "StdDraw.setXscale(0, n);\n",
    "StdDraw.setYscale(-1.5, 1.5);\n",
    "StdDraw.setPenColor(StdDraw.BLUE);\n",
    "for (int i = 0; i < n; i++) {\n",
    "    double x0 = i, y0 = Math.sin(i * 0.1);\n",
    "    double x1 = i + 1, y1 = Math.sin((i + 1) * 0.1);\n",
    "    StdDraw.line(x0, y0, x1, y1);\n",
    "}\n",
    "StdDraw.setPenColor(StdDraw.RED);\n",
    "StdDraw.text(n / 2.0, 1.2, \"y = sin(x)\");\n",
    "\n",
    "StdDraw.save(\"sin_plot.png\");   // 保存到当前目录\n",
    "StdOut.println(\"已保存 sin_plot.png\");"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 显示绘图结果"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "![sin曲线](sin_plot.png)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 第 3 步：音频 — StdAudio 合成一段旋律（八音盒）\n",
    "\n",
    "服务器无声卡，所以**合成样本保存为 WAV**，学生用浏览器 `<audio>` 播放。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "// 用 StdAudio 合成 \"小星星\" 的前几个音符 (C D E C)\n",
    "int sampleRate = 44100;\n",
    "double duration = 0.5;   // 每个音 0.5 秒\n",
    "int n = (int)(sampleRate * duration);\n",
    "\n",
    "// 频率映射: C4=261.63, D4=293.66, E4=329.63, G4=392.0\n",
    "double[] notes = {261.63, 293.66, 329.63, 261.63};\n",
    "\n",
    "double[] all = new double[notes.length * n];\n",
    "int idx = 0;\n",
    "for (double freq : notes) {\n",
    "    for (int i = 0; i < n; i++) {\n",
    "        double t = (double)i / sampleRate;\n",
    "        // 正弦波 + 衰减包络(模拟八音盒)\n",
    "        all[idx++] = Math.sin(2 * Math.PI * freq * t) * Math.exp(-4 * t);\n",
    "    }\n",
    "}\n",
    "\n",
    "StdAudio.save(\"twinkle.wav\", all);   // 保存合成音频\n",
    "StdOut.println(\"已合成并保存 twinkle.wav (\" + all.length + \" samples)\");"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 播放音频"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<audio controls src=\"twinkle.wav\"></audio>"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 第 4 步（进阶）：JFreeChart 像 matplotlib 那样画柱状图\n",
    "\n",
    "jjava 支持 `%maven` 拉依赖，这里用 JFreeChart 画成绩柱状图并在 notebook 内显示。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "%maven org.jfree:jfreechart:1.5.4\n",
    "import org.jfree.chart.*;\n",
    "import org.jfree.chart.plot.PlotOrientation;\n",
    "import org.jfree.data.category.DefaultCategoryDataset;\n",
    "import java.awt.image.BufferedImage;\n",
    "\n",
    "DefaultCategoryDataset ds = new DefaultCategoryDataset();\n",
    "ds.addValue(95, \"CSA\", \"Tina\");\n",
    "ds.addValue(88, \"CSA\", \"Kevin\");\n",
    "ds.addValue(92, \"CSA\", \"Gerben\");\n",
    "JFreeChart c = ChartFactory.createBarChart(\n",
    "    \"AP CSA 成绩\", \"学生\", \"分数\", ds, \n",
    "    PlotOrientation.VERTICAL, true, true, false);\n",
    "\n",
    "BufferedImage img = c.createBufferedImage(500, 350);\n",
    "img   // 直接在 notebook 显示 PNG"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "---\n",
    "### 作业思路（对标普林斯顿 COS 126）\n",
    "\n",
    "把这一页扩展成项目作业：\n",
    "- **N-Body / 分形绘图**：用 StdDraw 离屏渲染帧序列\n",
    "- **排序可视化**：画冒泡/快排过程\n",
    "- **音频项目**：合成一段完整旋律 / 音频频谱可视化\n",
    "- 每个作业 = 题目背景 + `// TODO` 代码cell + 测试cell + 自检清单"
   ]
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": "Java (jjava)",
   "language": "java",
   "name": "jjava"
  },
  "language_info": {
   "name": "java"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 5
}