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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>077. 买卖股票的最佳时机 – 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; }</style>
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</head>
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<body><div class="container">
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<h1>🟢 077. 买卖股票的最佳时机 <span class="badge easy">简单</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="[7,1,5,3,6,4]">
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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 maxProfit(prices):
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min_price = float('inf')
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max_profit = 0
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for i, price in enumerate(prices):
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if price < min_price:
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min_price = price # 更新最低价
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elif price - min_price > max_profit:
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max_profit = price - min_price # 更新最大利润
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return max_profit`;
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const EXAMPLES = [
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{ name: '例1: [7,1,5,3,6,4]', input: '[7,1,5,3,6,4]' },
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{ name: '例2: [7,6,4,3,1]', input: '[7,6,4,3,1]' },
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{ name: '例3: [2,4,1]', input: '[2,4,1]' },
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{ name: '例4: [3,2,6,5,0,3]', input: '[3,2,6,5,0,3]' },
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];
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let controller = null;
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function genSteps(prices) {
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const steps = [];
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let minPrice = Infinity;
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let minIdx = -1;
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let maxProfit = 0;
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let buyIdx = -1, sellIdx = -1;
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steps.push({
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desc: '初始化：min_price = ∞, max_profit = 0',
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hint: '遍历价格数组，维护历史最低价和最大利润差。',
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detail: '<b>思路</b>：只需一次遍历。<br>• 遇到更低价格 → 更新 min_price<br>• 否则计算 price - min_price，若更大则更新 max_profit<br><br>时间复杂度 O(n)，空间 O(1)',
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hlLine: -1,
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arrCls: prices.map(() => ''),
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arrTags: prices.map(() => ''),
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minIdx: -1, curIdx: -1,
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maxProfit: 0, bestBuy: -1, bestSell: -1,
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});
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prices.forEach((price, i) => {
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const arrCls = prices.map(() => '');
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const arrTags = prices.map(() => '');
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if (minIdx >= 0) arrCls[minIdx] = 'min-price';
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arrCls[i] = 'current';
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if (price < minPrice) {
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const oldMin = minPrice;
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minPrice = price;
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minIdx = i;
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arrCls[minIdx] = 'min-price';
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arrTags[minIdx] = '最低';
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steps.push({
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desc: `i=${i}: prices[${i}] = ${price} < ${oldMin === Infinity ? '∞' : oldMin} → 更新最低价`,
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hint: `发现更低价格 ${price}，更新 min_price。此时卖出不产生利润，继续寻找更高卖价。`,
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detail: `prices[${i}] = <b>${price}</b><br>当前 min_price: ${oldMin === Infinity ? '∞' : oldMin} → <b>${minPrice}</b><br>max_profit 不变 = ${maxProfit}`,
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hlLine: 4,
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arrCls: [...arrCls], arrTags: [...arrTags],
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minIdx, curIdx: i, maxProfit, bestBuy, bestSell,
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});
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} else {
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const profit = price - minPrice;
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if (profit > maxProfit) {
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maxProfit = profit;
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buyIdx = minIdx;
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sellIdx = i;
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arrCls[sellIdx] = 'best';
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arrTags[sellIdx] = '利润' + profit;
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if (buyIdx >= 0) { arrCls[buyIdx] = 'min-price'; arrTags[buyIdx] = '买入'; }
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steps.push({
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desc: `i=${i}: prices[${i}] = ${price}，利润 ${price} - ${minPrice} = ${profit} > ${maxProfit - profit === 0 && profit > 0 ? 0 : maxProfit - profit} → 更新最大利润`,
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hint: `当前利润 ${profit} 超过之前最大利润，更新 max_profit = ${profit}。`,
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detail: `prices[${i}] = <b>${price}</b><br>利润 = ${price} - ${minPrice} = <b>${profit}</b><br>max_profit 更新为 <b>${maxProfit}</b><br>买入: prices[${buyIdx}] = ${prices[buyIdx]}，卖出: prices[${sellIdx}] = ${prices[sellIdx]}`,
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hlLine: 6,
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arrCls: [...arrCls], arrTags: [...arrTags],
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minIdx, curIdx: i, maxProfit, bestBuy: buyIdx, bestSell: sellIdx,
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});
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} else {
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steps.push({
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desc: `i=${i}: prices[${i}] = ${price}，利润 ${profit} ≤ ${maxProfit} → 不更新`,
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hint: `当前利润 ${profit} 未超过 max_profit(${maxProfit})，保持不变。`,
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detail: `prices[${i}] = <b>${price}</b><br>利润 = ${price} - ${minPrice} = ${profit}<br>max_profit 不变 = ${maxProfit}`,
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hlLine: 6,
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arrCls: [...arrCls], arrTags: [...arrTags],
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minIdx, curIdx: i, maxProfit, bestBuy: buyIdx, bestSell: sellIdx,
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});
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}
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}
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});
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// final
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const finalCls = prices.map(() => '');
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const finalTags = prices.map(() => '');
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if (bestBuy >= 0) { finalCls[bestBuy] = 'min-price'; finalTags[bestBuy] = '买入'; }
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if (bestSell >= 0) { finalCls[bestSell] = 'best'; finalTags[bestSell] = '卖出'; }
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steps.push({
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desc: `遍历结束，最大利润 = ${maxProfit}`,
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hint: maxProfit > 0 ? `在 prices[${buyIdx}]=${prices[buyIdx]} 买入，prices[${sellIdx}]=${prices[sellIdx]} 卖出，利润 = ${maxProfit}` : '价格持续下降，无法获得正利润，返回 0',
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detail: `<b>最终结果</b>：max_profit = <b>${maxProfit}</b>${maxProfit > 0 ? `<br>买入点: i=${buyIdx}, price=${prices[buyIdx]}<br>卖出点: i=${sellIdx}, price=${prices[sellIdx]}` : ''}`,
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hlLine: -1,
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arrCls: finalCls, arrTags: finalTags,
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minIdx, curIdx: -1, maxProfit, bestBuy: buyIdx, bestSell: sellIdx,
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isFinal: true,
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});
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return steps;
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}
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function renderStep(step) {
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if (!step) {
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$('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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// pipeline info
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$('stepInfo').textContent = step.desc;
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$('hintText').textContent = step.hint;
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$('detailContent').innerHTML = step.detail;
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// render array
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const prices = parseInput($('inputArea').value);
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const items = prices.map((p, i) => ({ val: p, cls: step.arrCls[i] || '', tag: step.arrTags[i] || '' }));
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renderArray($('vizArea'), items, { barMaxH: 140, barMinW: 36 });
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// add legend
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const legend = document.createElement('div');
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legend.className = 'legend';
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legend.innerHTML = `
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<span class="legend-item"><span class="legend-dot" style="background:var(--green)"></span> 最低价/买入</span>
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<span class="legend-item"><span class="legend-dot" style="background:var(--orange)"></span> 当前遍历</span>
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<span class="legend-item"><span class="legend-dot" style="background:var(--accent)"></span> 卖出/最大利润</span>
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`;
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$('vizArea').appendChild(legend);
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// stats
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const stats = document.createElement('div');
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stats.style.cssText = 'text-align:center;margin-top:12px;font-family:var(--mono);font-size:.85rem;';
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stats.innerHTML = `min_price = <span style="color:var(--green)">${step.minIdx >= 0 ? prices[step.minIdx] : '∞'}</span> max_profit = <span style="color:var(--orange)">${step.maxProfit}</span>`;
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$('vizArea').appendChild(stats);
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// code highlight
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renderCode($('codeArea'), CODE, step.hlLine);
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// result
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if (step.isFinal) {
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$('resultContent').innerHTML = `<div class="result-box">最大利润 = <span class="val">${step.maxProfit}</span>${step.bestBuy >= 0 ? `<br><small>买入 prices[${step.bestBuy}]=${prices[step.bestBuy]}，卖出 prices[${step.bestSell}]=${prices[step.bestSell]}</small>` : '<br><small>无正利润交易</small>'}</div>`;
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} else {
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$('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 [7,1,5,3,6,4];
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}
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function build() {
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const prices = parseInput($('inputArea').value);
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const steps = genSteps(prices);
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if (controller) controller.stopAuto();
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controller = new StepController(steps, { onRender: renderStep });
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$('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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