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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>093. 最长回文子串 – 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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.expansion-line{display:flex;margin-top:4px;justify-content:center;font-family:var(--mono);font-size:.75rem;color:var(--text2);}
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.bracket{padding:0 2px;}
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.arrow-l,.arrow-r{color:var(--orange);font-weight:700;}
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</style>
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</head>
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<body><div class="container">
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<h1>🟡 093. 最长回文子串 <span class="badge medium">中等</span></h1>
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<p class="subtitle">分类：字符串 ｜ 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="babad">
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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 longestPalindrome(s):
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def expand(l, r):
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while l >= 0 and r < len(s) and s[l] == s[r]:
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l -= 1
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r += 1
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return l + 1, r - 1 # 回文起止
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best_l, best_r = 0, 0
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for i in range(len(s)):
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# 奇数长度
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l1, r1 = expand(i, i)
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if r1 - l1 > best_r - best_l:
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best_l, best_r = l1, r1
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# 偶数长度
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l2, r2 = expand(i, i + 1)
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if r2 - l2 > best_r - best_l:
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best_l, best_r = l2, r2
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return s[best_l:best_r+1]`;
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const EXAMPLES = [
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{ name: '例1: babad', input: 'babad' },
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{ name: '例2: cbbd', input: 'cbbd' },
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{ name: '例3: a', input: 'a' },
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{ name: '例4: racecar', input: 'racecar' },
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{ name: '例5: abacdfgdcaba', input: 'abacdfgdcaba' },
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];
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let controller = null;
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function expandAroundCenter(s, l, r) {
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const steps = [];
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while (l >= 0 && r < s.length && s[l] === s[r]) {
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steps.push({ l, r, matched: true });
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l--; r++;
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}
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steps.push({ l: l + 1, r: r - 1, matched: false, isFinal: true });
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return steps;
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}
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function genSteps(s) {
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const steps = [];
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const n = s.length;
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let bestL = 0, bestR = 0;
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steps.push({
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desc: '初始化：对每个位置做中心扩展',
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hint: '枚举每个中心位置，向两侧扩展，找到最长回文。',
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detail: '<b>思路</b>：中心扩展法<br>• 对每个下标 i，分别以 (i,i) 和 (i,i+1) 为中心<br>• 向两侧扩展直到不等<br>• 记录最长回文的起止位置<br><br>时间 O(n²)，空间 O(1)',
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hlLine: -1, centerIdx: -1, centerType: '',
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expL: -1, expR: -1, bestL: 0, bestR: 0,
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cellCls: s.split('').map(() => ''),
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});
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for (let i = 0; i < n; i++) {
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// odd length
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const oddSteps = expandAroundCenter(s, i, i);
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for (const es of oddSteps) {
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const cellCls = s.split('').map(() => '');
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// mark palindrome range
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if (es.l >= 0 && es.r < n) {
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for (let j = es.l; j <= es.r; j++) cellCls[j] = 'palindrome';
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}
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// mark center
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cellCls[i] = 'center';
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// mark expansion pointers
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if (es.l !== i || es.r !== i) {
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if (es.l >= 0) cellCls[es.l] = es.matched ? 'expand' : 'palindrome';
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if (es.r < n) cellCls[es.r] = es.matched ? 'expand' : 'palindrome';
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}
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// mark best
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for (let j = bestL; j <= bestR; j++) cellCls[j] = 'best';
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// but center takes priority visual
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if (es.isFinal) {
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const newBest = es.r - es.l > bestR - bestL;
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if (newBest) { bestL = es.l; bestR = es.r; }
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steps.push({
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desc: `中心 i=${i}（奇数）：扩展到 [${es.l}, ${es.r}]，回文 "${s.substring(es.l, es.r + 1)}"${newBest ? ' → 更新最优！' : ''}`,
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hint: newBest ? `找到更长回文 "${s.substring(es.l, es.r + 1)}"（长度 ${es.r - es.l + 1}）` : `回文长度 ${es.r - es.l + 1}，未超过当前最优 ${bestR - bestL + 1}`,
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detail: `中心 i=<b>${i}</b>（奇数长度）<br>扩展结果：[${es.l}, ${es.r}] = "${s.substring(es.l, es.r + 1)}"<br>长度 = ${es.r - es.l + 1}${newBest ? '<br><span style="color:var(--green)">更新最优！</span>' : '<br>未超过当前最优 ' + (bestR - bestL + 1)}`,
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hlLine: 10,
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centerIdx: i, centerType: 'odd',
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expL: es.l, expR: es.r, bestL, bestR,
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cellCls,
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});
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} else {
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steps.push({
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desc: `中心 i=${i}（奇数）：s[${es.l}]='${s[es.l]}' == s[${es.r}]='${s[es.r]}'，扩展到 [${es.l}, ${es.r}]`,
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hint: `字符匹配，继续向外扩展。`,
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detail: `中心 i=<b>${i}</b>（奇数）<br>比较 s[${es.l}]='${s[es.l]}' ↔ s[${es.r}]='${s[es.r]}'<br>✅ 匹配！范围 [${es.l}, ${es.r}]`,
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hlLine: 3,
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centerIdx: i, centerType: 'odd',
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expL: es.l, expR: es.r, bestL, bestR,
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cellCls,
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});
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}
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}
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// even length
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if (i + 1 < n) {
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const evenSteps = expandAroundCenter(s, i, i + 1);
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for (const es of evenSteps) {
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const cellCls = s.split('').map(() => '');
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if (es.l >= 0 && es.r < n) {
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for (let j = es.l; j <= es.r; j++) cellCls[j] = 'palindrome';
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}
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cellCls[i] = 'center';
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if (i + 1 < n) cellCls[i + 1] = 'center';
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if (es.l !== i || es.r !== i + 1) {
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if (es.l >= 0 && es.l !== i) cellCls[es.l] = es.matched ? 'expand' : 'palindrome';
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if (es.r < n && es.r !== i + 1) cellCls[es.r] = es.matched ? 'expand' : 'palindrome';
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}
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for (let j = bestL; j <= bestR; j++) cellCls[j] = 'best';
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if (es.isFinal) {
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const newBest = es.r - es.l > bestR - bestL;
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if (newBest) { bestL = es.l; bestR = es.r; }
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steps.push({
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desc: `中心 i=${i},${i+1}（偶数）：扩展到 [${es.l}, ${es.r}]，回文 "${s.substring(es.l, es.r + 1)}"${newBest ? ' → 更新最优！' : ''}`,
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hint: newBest ? `找到更长回文 "${s.substring(es.l, es.r + 1)}"（长度 ${es.r - es.l + 1}）` : `回文长度 ${es.r - es.l + 1}，未超过当前最优 ${bestR - bestL + 1}`,
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detail: `中心 i=<b>${i},${i+1}</b>（偶数长度）<br>扩展结果：[${es.l}, ${es.r}] = "${s.substring(es.l, es.r + 1)}"<br>长度 = ${es.r - es.l + 1}${newBest ? '<br><span style="color:var(--green)">更新最优！</span>' : '<br>未超过当前最优 ' + (bestR - bestL + 1)}`,
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hlLine: 12,
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centerIdx: i, centerType: 'even',
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expL: es.l, expR: es.r, bestL, bestR,
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cellCls,
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});
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} else {
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steps.push({
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desc: `中心 i=${i},${i+1}（偶数）：s[${es.l}]='${s[es.l]}' == s[${es.r}]='${s[es.r]}'，扩展到 [${es.l}, ${es.r}]`,
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hint: `字符匹配，继续向外扩展。`,
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detail: `中心 i=<b>${i},${i+1}</b>（偶数）<br>比较 s[${es.l}]='${s[es.l]}' ↔ s[${es.r}]='${s[es.r]}'<br>✅ 匹配！范围 [${es.l}, ${es.r}]`,
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hlLine: 3,
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centerIdx: i, centerType: 'even',
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expL: es.l, expR: es.r, bestL, bestR,
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cellCls,
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});
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}
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}
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}
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}
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// final
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const finalCls = s.split('').map(() => '');
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for (let j = bestL; j <= bestR; j++) finalCls[j] = 'best';
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steps.push({
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desc: `遍历结束，最长回文子串 = "${s.substring(bestL, bestR + 1)}"`,
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hint: '中心扩展法穷举了所有可能的回文中心。',
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detail: `<b>结果</b>：最长回文子串 = <b>"${s.substring(bestL, bestR + 1)}"</b><br>位置：[${bestL}, ${bestR}]<br>长度：${bestR - bestL + 1}`,
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hlLine: -1, centerIdx: -1, centerType: '',
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expL: bestL, expR: bestR, bestL, bestR,
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cellCls: finalCls, result: s.substring(bestL, bestR + 1), 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 = $('resultContent').innerHTML = '';
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$('stepInfo').textContent = $('hintText').textContent = '';
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return;
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}
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$('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 s = $('inputArea').value.trim();
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// string cells
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const row = document.createElement('div');
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row.className = 'str-row';
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s.split('').forEach((c, i) => {
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const cell = document.createElement('div');
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const cls = step.cellCls[i] || '';
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cell.className = 'str-cell ' + cls;
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cell.innerHTML = `${c}<span class="str-idx">${i}</span>`;
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row.appendChild(cell);
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});
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$('vizArea').innerHTML = '';
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$('vizArea').appendChild(row);
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// expansion arrows
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if (step.expL >= 0 && step.expR >= 0 && step.centerIdx >= 0) {
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const arrow = document.createElement('div');
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arrow.className = 'expansion-line';
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const ptrs = s.split('').map((_, i) => {
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if (i === step.expL && i === step.expR) return '<span style="color:var(--orange)">▲</span>';
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if (i === step.expL) return '<span class="arrow-l">◀</span>';
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if (i === step.expR) return '<span class="arrow-r">▶</span>';
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return ' ';
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});
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arrow.innerHTML = ptrs.join(' ');
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$('vizArea').appendChild(arrow);
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}
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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:8px;font-family:var(--mono);font-size:.82rem;';
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const best = step.bestR - step.bestL + 1;
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stats.innerHTML = `当前最优 = <span style="color:var(--green)">"${s.substring(step.bestL, step.bestR + 1)}"</span>（长度 ${best}）`;
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$('vizArea').appendChild(stats);
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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(--orange)"></span> 中心位置</span>
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<span class="legend-item"><span class="legend-dot" style="background:var(--purple)"></span> 扩展边界</span>
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<span class="legend-item"><span class="legend-dot" style="background:var(--green)"></span> 最长回文</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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$('resultContent').innerHTML = `<div class="result-box">最长回文子串 = <span class="val">"${step.result}"</span><br><small>位置 [${step.bestL}, ${step.bestR}]，长度 ${step.bestR - step.bestL + 1}</small></div>`;
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} else {
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$('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 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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function build() {
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const s = $('inputArea').value.trim();
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const steps = genSteps(s);
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if (controller) controller.stopAuto();
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controller = new StepController(steps, { onRender: renderStep });
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$('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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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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Reference in New Issue
Block a user