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<!DOCTYPE html>
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<html lang="zh-Hans">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>078. 跳跃游戏 – 图解</title>
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<link rel="stylesheet" href="../shared/style.css">
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<style>.vis-area { min-height: 120px; padding: 16px 0; } .code-section { margin-top: 16px; }
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.reach-bar{height:6px;border-radius:3px;margin-top:8px;background:var(--surface2);position:relative;overflow:hidden;}
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.reach-fill{height:100%;border-radius:3px;background:linear-gradient(90deg,var(--blue),var(--green));transition:width .3s;}
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</style>
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</head>
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<body><div class="container">
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<h1>🟡 078. 跳跃游戏 <span class="badge medium">中等</span></h1>
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<p class="subtitle">分类：贪心 ｜ LeetCode Hot 100</p>
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<div class="controls" id="controls">
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<label>输入：</label><input type="text" id="inputArea" value="[2,3,1,1,4]">
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<button id="applyBtn" class="primary">生成图解</button>
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<select id="exampleSelect"></select>
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<span style="flex:1"></span>
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<button id="prevBtn">◀ 上一步</button>
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<button id="nextBtn">下一步 ▶</button>
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<button id="jumpBtn">⏭ 跳到结果</button>
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<button id="autoBtn">自动播放</button>
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<button id="resetBtn">重置</button>
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</div>
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<div class="pipeline" id="pipeline"></div>
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<div class="hint info" id="hintBox"><span id="stepInfo"></span><br><span id="hintText"></span></div>
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<div class="panels">
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<div class="panel" id="mainPanel"><h3>📊 可视化</h3><div class="vis-area" id="vizArea"></div></div>
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<div class="panel-grid">
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<div class="panel" id="detailPanel"><h3>📝 当前步骤详情</h3><div id="detailContent"></div></div>
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<div class="panel" id="resultPanel"><h3>✅ 结果</h3><div id="resultContent"></div></div>
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</div>
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</div>
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<div class="panel code-section"><h3>💻 参考代码（Python）</h3><div id="codeArea"></div></div>
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<footer>Powered by QwenPaw · 图解算法 · LeetCode Hot 100</footer>
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</div>
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<script src="../shared/algo-viz.js"></script>
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<script>"use strict";(function(){
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const CODE = `def canJump(nums):
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max_reach = 0
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for i, num in enumerate(nums):
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if i > max_reach: # 当前位置不可达
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return False
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max_reach = max(max_reach, i + num)
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if max_reach >= len(nums) - 1:
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return True
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return True`;
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const EXAMPLES = [
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{ name: '例1: [2,3,1,1,4]', input: '[2,3,1,1,4]' },
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{ name: '例2: [3,2,1,0,4]', input: '[3,2,1,0,4]' },
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{ name: '例3: [0]', input: '[0]' },
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{ name: '例4: [1,2,3]', input: '[1,2,3]' },
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];
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let controller = null;
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function genSteps(nums) {
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const steps = [];
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const n = nums.length;
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let maxReach = 0;
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let result = null;
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steps.push({
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desc: '初始化：maxReach = 0',
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hint: '贪心维护最远可达位置 maxReach，若遍历到 i > maxReach 说明不可达。',
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detail: '<b>思路</b>：遍历数组，维护最远可达下标。<br>• 若 i ≤ maxReach，位置可达，更新 maxReach = max(maxReach, i + nums[i])<br>• 若 i > maxReach，当前位置不可达，返回 False<br><br>时间 O(n)，空间 O(1)',
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hlLine: -1,
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curIdx: -1, maxReach: 0, result: null,
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});
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for (let i = 0; i < n; i++) {
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if (i > maxReach) {
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steps.push({
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desc: `i=${i} > maxReach=${maxReach}，位置不可达！`,
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hint: `当前位置 ${i} 超出最远可达范围 ${maxReach}，无法继续前进。`,
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detail: `i = <b>${i}</b>, maxReach = <b>${maxReach}</b><br>i > maxReach → 不可达<br>返回 <b>False</b>`,
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hlLine: 3,
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curIdx: i, maxReach, result: false,
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});
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result = false;
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break;
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}
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const newReach = Math.max(maxReach, i + nums[i]);
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const canFinish = newReach >= n - 1;
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steps.push({
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desc: `i=${i}: nums[${i}]=${nums[i]}，可达范围 ${i}+${nums[i]}=${i + nums[i]}，maxReach: ${maxReach} → ${newReach}${canFinish ? ' ≥ ' + (n-1) + ' → 可达终点！' : ''}`,
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hint: canFinish ? `最远可达 ${newReach} 已超终点，返回 True！` : `更新 maxReach = ${newReach}，继续遍历。`,
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detail: `i = <b>${i}</b>, nums[${i}] = <b>${nums[i]}</b><br>可达范围 = i + nums[i] = ${i + nums[i]}<br>maxReach: ${maxReach} → <b>${newReach}</b>${canFinish ? '<br><span style="color:var(--green)">maxReach ≥ ' + (n-1) + ' → 可达终点！</span>' : ''}`,
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hlLine: canFinish ? 6 : 5,
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curIdx: i, maxReach: newReach, result: canFinish ? true : null,
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});
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maxReach = newReach;
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if (canFinish) { result = true; break; }
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}
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if (result === null) {
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steps.push({
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desc: '遍历结束，可达终点',
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hint: '所有位置都在可达范围内，返回 True。',
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detail: '遍历完成，未遇到不可达位置。<br>返回 <b>True</b>',
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hlLine: 8,
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curIdx: -1, maxReach, result: true,
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});
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}
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// final
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steps.push({
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desc: `最终结果：${result ? '可以' : '不可以'}到达最后一个下标`,
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hint: result ? '贪心策略确保了只要可达，就能到达终点。' : '中间存在 0 且无法跳过，导致断裂。',
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detail: `<b>结果</b>：${result ? '<span style="color:var(--green)">True</span>' : '<span style="color:var(--red)">False</span>'}<br>maxReach 最终 = ${maxReach}`,
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hlLine: -1,
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curIdx: -1, maxReach, result, isFinal: true,
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});
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return steps;
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}
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function renderStep(step) {
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if (!step) {
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$('vizArea').innerHTML = '<div style="color:var(--text2);text-align:center;padding:40px;">点击「生成图解」开始</div>';
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$('detailContent').innerHTML = '';
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$('resultContent').innerHTML = '';
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$('stepInfo').textContent = '';
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$('hintText').textContent = '';
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return;
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}
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$('stepInfo').textContent = step.desc;
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$('hintText').textContent = step.hint;
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$('detailContent').innerHTML = step.detail;
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const nums = parseInput($('inputArea').value);
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const n = nums.length;
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// render chips
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const row = document.createElement('div');
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row.className = 'jump-row';
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nums.forEach((val, i) => {
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const cell = document.createElement('div');
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let cls = 'jump-cell';
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if (i === step.curIdx) cls += ' current';
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if (i <= step.maxReach && step.maxReach >= 0) cls += ' reachable';
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if (i === step.maxReach && step.curIdx !== i) cls += ' max-reach';
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cell.className = cls;
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cell.innerHTML = `<div class="j-chip">${val}</div><div class="j-idx">${i}</div>`;
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row.appendChild(cell);
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});
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$('vizArea').innerHTML = '';
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$('vizArea').appendChild(row);
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// reach bar
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const bar = document.createElement('div');
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bar.className = 'reach-bar';
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const fill = document.createElement('div');
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fill.className = 'reach-fill';
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fill.style.width = (step.maxReach >= 0 ? Math.min(100, ((step.maxReach + 1) / n) * 100) : 0) + '%';
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bar.appendChild(fill);
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$('vizArea').appendChild(bar);
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// legend + stats
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const info = document.createElement('div');
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info.style.cssText = 'text-align:center;margin-top:10px;font-family:var(--mono);font-size:.82rem;';
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info.innerHTML = `maxReach = <span style="color:var(--green)">${step.maxReach}</span> / ${n - 1}${step.result === true ? ' ✅ 可达终点' : step.result === false ? ' ❌ 不可达' : ''}`;
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$('vizArea').appendChild(info);
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const legend = document.createElement('div');
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legend.className = 'legend';
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legend.innerHTML = `
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<span class="legend-item"><span class="legend-dot" style="background:var(--blue)"></span> 可达范围</span>
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<span class="legend-item"><span class="legend-dot" style="background:var(--orange)"></span> 当前位置</span>
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<span class="legend-item"><span class="legend-dot" style="background:var(--green)"></span> 最远可达</span>
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`;
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$('vizArea').appendChild(legend);
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renderCode($('codeArea'), CODE, step.hlLine);
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if (step.isFinal) {
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const r = step.result;
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$('resultContent').innerHTML = `<div class="result-box" style="${r ? '' : 'background:var(--red-dim);border-color:rgba(240,96,96,.3);color:var(--red);'}">结果 = <span class="val">${r ? 'True' : 'False'}</span><br><small>${r ? '可以到达最后一个下标' : '无法到达最后一个下标'}</small></div>`;
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} else {
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$('resultContent').innerHTML = `<div style="color:var(--text2);font-size:.85rem;">等待遍历完成…</div>`;
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}
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}
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function parseInput(s) {
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try {
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const a = JSON.parse(s.replace(/'/g, '"'));
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if (Array.isArray(a) && a.every(x => typeof x === 'number')) return a;
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} catch(e) {}
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return [2,3,1,1,4];
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}
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function build() {
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const nums = parseInput($('inputArea').value);
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const steps = genSteps(nums);
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if (controller) controller.stopAuto();
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controller = new StepController(steps, { onRender: renderStep });
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$('nextBtn').onclick = () => controller.next();
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$('prevBtn').onclick = () => controller.prev();
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$('jumpBtn').onclick = () => controller.jumpEnd();
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$('resetBtn').onclick = () => controller.reset();
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$('autoBtn').onclick = () => { if (controller.autoTimer) controller.stopAuto(); else controller.startAuto(); };
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controller.next();
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}
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function init() {
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const sel = $('exampleSelect');
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EXAMPLES.forEach((ex, i) => {
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const o = document.createElement('option');
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o.value = i; o.textContent = ex.name;
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sel.appendChild(o);
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});
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sel.onchange = () => { $('inputArea').value = EXAMPLES[sel.value].input; build(); };
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$('applyBtn').onclick = build;
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$('inputArea').onkeydown = e => { if (e.key === 'Enter') build(); };
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build();
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}
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if (document.readyState === 'loading') document.addEventListener('DOMContentLoaded', init);
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else init();
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})()</script>
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</body></html>
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