{"id":369,"date":"2025-09-08T11:04:14","date_gmt":"2025-09-08T03:04:14","guid":{"rendered":"https:\/\/heyingnian.com\/?p=369"},"modified":"2025-09-08T11:04:35","modified_gmt":"2025-09-08T03:04:35","slug":"leetcode-142","status":"publish","type":"post","link":"https:\/\/heyingnian.com\/index.php\/2025\/09\/08\/leetcode-142\/","title":{"rendered":"\u73af\u5f62\u94fe\u8868 II\uff1a\u5bfb\u627e\u73af\u7684\u5165\u53e3"},"content":{"rendered":"\n<h1 class=\"wp-block-heading\">\ud83d\udd17 \u73af\u5f62\u94fe\u8868 II\uff1a\u5bfb\u627e\u73af\u7684\u5165\u53e3<\/h1>\n\n\n\n<p>\u9898\u76ee\u6765\u6e90\uff1a<a target=\"_blank\" rel=\"noreferrer noopener\"><a href=\"https:\/\/leetcode.cn\/problems\/linked-list-cycle-ii\/?envType=study-plan-v2&amp;envId=top-100-liked\" target=\"_blank\" rel=\"noopener\">142. \u73af\u5f62\u94fe\u8868 II &#8211; \u529b\u6263\uff08LeetCode\uff09<\/a><\/a><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p>\ud83d\udccc \u9898\u76ee\u63cf\u8ff0<\/p>\n\n\n\n<p>\u7ed9\u5b9a\u4e00\u4e2a\u94fe\u8868\u7684\u5934\u8282\u70b9 <code>head<\/code>\uff0c\u8fd4\u56de\u94fe\u8868\u5f00\u59cb\u5165\u73af\u7684\u7b2c\u4e00\u4e2a\u8282\u70b9\u3002\u5982\u679c\u94fe\u8868\u65e0\u73af\uff0c\u5219\u8fd4\u56de <code>null<\/code>\u3002<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u4e0d\u5141\u8bb8\u4fee\u6539\u94fe\u8868\u7ed3\u6784<\/strong>\u3002<\/li>\n\n\n\n<li><strong>\u4e0d\u80fd\u4f7f\u7528\u989d\u5916\u7684\u54c8\u5e0c\u8868\u5b58\u50a8\u8282\u70b9<\/strong>\u3002<\/li>\n<\/ul>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p>\u26a0\ufe0f \u6ce8\u610f\uff1a\u8f93\u5165\u4e2d\u7684 <code>pos<\/code> \u4ec5\u7528\u4e8e\u6807\u8bc6\u73af\u7684\u8d77\u59cb\u4f4d\u7f6e\uff0c<strong>\u4e0d\u4f5c\u4e3a\u53c2\u6570\u4f20\u5165\u51fd\u6570<\/strong>\u3002<\/p>\n<\/blockquote>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p>\u2705 \u793a\u4f8b\u89e3\u6790<\/p>\n\n\n\n<p><strong>\u793a\u4f8b 1<\/strong>\uff1a<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><div class='fancybox-wrapper lazyload-container-unload' data-fancybox='post-images' href='https:\/\/heyingnian.com\/wp-content\/uploads\/2025\/09\/image-18.png'><img class=\"lazyload lazyload-style-1\" src=\"data:image\/svg+xml;base64,PCEtLUFyZ29uTG9hZGluZy0tPgo8c3ZnIHdpZHRoPSIxIiBoZWlnaHQ9IjEiIHhtbG5zPSJodHRwOi8vd3d3LnczLm9yZy8yMDAwL3N2ZyIgc3Ryb2tlPSIjZmZmZmZmMDAiPjxnPjwvZz4KPC9zdmc+\"  loading=\"lazy\" decoding=\"async\" width=\"531\" height=\"171\" data-original=\"https:\/\/heyingnian.com\/wp-content\/uploads\/2025\/09\/image-18.png\" src=\"data:image\/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB\/AAffA0nNPuCLAAAAAElFTkSuQmCC\" alt=\"\" class=\"wp-image-370\"  sizes=\"auto, (max-width: 531px) 100vw, 531px\" \/><\/div><\/figure>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u8f93\u5165\uff1a<code>head = [3,2,0,-4]<\/code>,\u00a0<code>pos = 1<\/code><\/li>\n\n\n\n<li>\u8f93\u51fa\uff1a\u8fd4\u56de\u503c\u4e3a\u7d22\u5f15\u00a0<code>1<\/code>\u00a0\u7684\u8282\u70b9\uff08\u5373\u503c\u4e3a\u00a0<code>2<\/code>\u00a0\u7684\u8282\u70b9\uff09<\/li>\n\n\n\n<li>\u89e3\u91ca\uff1a\u94fe\u8868\u5c3e\u90e8\uff08<code>-4<\/code>\uff09\u8fde\u63a5\u5230\u7d22\u5f15\u4e3a\u00a0<code>1<\/code>\u00a0\u7684\u8282\u70b9\uff0c\u5f62\u6210\u73af\u3002<\/li>\n<\/ul>\n\n\n\n<p><strong>\u793a\u4f8b 2<\/strong>\uff1a<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><div class='fancybox-wrapper lazyload-container-unload' data-fancybox='post-images' href='https:\/\/heyingnian.com\/wp-content\/uploads\/2025\/09\/image-19.png'><img class=\"lazyload lazyload-style-1\" src=\"data:image\/svg+xml;base64,PCEtLUFyZ29uTG9hZGluZy0tPgo8c3ZnIHdpZHRoPSIxIiBoZWlnaHQ9IjEiIHhtbG5zPSJodHRwOi8vd3d3LnczLm9yZy8yMDAwL3N2ZyIgc3Ryb2tlPSIjZmZmZmZmMDAiPjxnPjwvZz4KPC9zdmc+\"  loading=\"lazy\" decoding=\"async\" width=\"201\" height=\"105\" data-original=\"https:\/\/heyingnian.com\/wp-content\/uploads\/2025\/09\/image-19.png\" src=\"data:image\/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB\/AAffA0nNPuCLAAAAAElFTkSuQmCC\" alt=\"\" class=\"wp-image-371\"\/><\/div><\/figure>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u8f93\u5165\uff1a<code>head = [1,2]<\/code>,\u00a0<code>pos = 0<\/code><\/li>\n\n\n\n<li>\u8f93\u51fa\uff1a\u8fd4\u56de\u503c\u4e3a\u7d22\u5f15\u00a0<code>0<\/code>\u00a0\u7684\u8282\u70b9\uff08\u5373\u5934\u8282\u70b9\u00a0<code>1<\/code>\uff09<\/li>\n\n\n\n<li>\u89e3\u91ca\uff1a\u5c3e\u90e8\u8fde\u63a5\u5230\u5934\u8282\u70b9\uff0c\u5f62\u6210\u73af\u3002<\/li>\n<\/ul>\n\n\n\n<p><strong>\u793a\u4f8b 3<\/strong>\uff1a<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><div class='fancybox-wrapper lazyload-container-unload' data-fancybox='post-images' href='https:\/\/heyingnian.com\/wp-content\/uploads\/2025\/09\/image-20.png'><img class=\"lazyload lazyload-style-1\" src=\"data:image\/svg+xml;base64,PCEtLUFyZ29uTG9hZGluZy0tPgo8c3ZnIHdpZHRoPSIxIiBoZWlnaHQ9IjEiIHhtbG5zPSJodHRwOi8vd3d3LnczLm9yZy8yMDAwL3N2ZyIgc3Ryb2tlPSIjZmZmZmZmMDAiPjxnPjwvZz4KPC9zdmc+\"  loading=\"lazy\" decoding=\"async\" width=\"65\" height=\"65\" data-original=\"https:\/\/heyingnian.com\/wp-content\/uploads\/2025\/09\/image-20.png\" src=\"data:image\/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB\/AAffA0nNPuCLAAAAAElFTkSuQmCC\" alt=\"\" class=\"wp-image-372\"  sizes=\"auto, (max-width: 65px) 100vw, 65px\" \/><\/div><\/figure>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u8f93\u5165\uff1a<code>head = [1]<\/code>,\u00a0<code>pos = -1<\/code><\/li>\n\n\n\n<li>\u8f93\u51fa\uff1a<code>null<\/code><\/li>\n\n\n\n<li>\u89e3\u91ca\uff1a\u65e0\u73af\u3002<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p>\u26a0\ufe0f \u63d0\u793a<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u94fe\u8868\u4e2d\u8282\u70b9\u7684\u6570\u76ee\u8303\u56f4\u5728\u00a0<code>[0, 10\u2074]<\/code>\u00a0\u5185<\/li>\n\n\n\n<li><code>-10\u2075 &lt;= Node.val &lt;= 10\u2075<\/code><\/li>\n\n\n\n<li><code>pos<\/code>\u00a0\u7684\u503c\u4e3a\u00a0<code>-1<\/code>\u00a0\u6216\u94fe\u8868\u4e2d\u7684\u4e00\u4e2a\u6709\u6548\u7d22\u5f15<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p>\ud83d\udca1 \u89e3\u6cd5\uff1a\u5feb\u6162\u6307\u9488 + \u6570\u5b66\u63a8\u5bfc \u2014\u2014 O(n) \u65f6\u95f4\uff0cO(1) \u7a7a\u95f4<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>public class Solution {\n    public ListNode detectCycle(ListNode head) {\n        ListNode fast = head;\n        ListNode slow = head;\n        while (fast != null &amp;&amp; fast.next != null) {\n            fast = fast.next.next;\n            slow = slow.next;\n            if (fast == slow) {\n                break; \n            }\n        }\n        if (fast == null || fast.next == null) {\n            return null; \n        }\n        slow = head;\n        while (slow != fast) {\n            slow = slow.next;\n            fast = fast.next;\n        }\n        return slow;\n    }\n}<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p>\ud83d\udcca \u590d\u6742\u5ea6\u5206\u6790<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u65f6\u95f4\u590d\u6742\u5ea6\uff1aO(n)<\/strong>\n<ul class=\"wp-block-list\">\n<li>\u7b2c\u4e00\u9636\u6bb5\u627e\u76f8\u9047\u70b9\uff1aO(n)<\/li>\n\n\n\n<li>\u7b2c\u4e8c\u9636\u6bb5\u627e\u73af\u5165\u53e3\uff1aO(n)<\/li>\n\n\n\n<li>\u603b\u4f53\u7ebf\u6027\u65f6\u95f4\u3002<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>\u7a7a\u95f4\u590d\u6742\u5ea6\uff1aO(1)<\/strong> \u2705\n<ul class=\"wp-block-list\">\n<li>\u4ec5\u4f7f\u7528\u4e24\u4e2a\u6307\u9488\uff0c\u65e0\u989d\u5916\u7a7a\u95f4\u3002<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p>\ud83e\udde9 \u89e3\u9898\u601d\u8def<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>\u6838\u5fc3\u601d\u60f3\uff1a\u5feb\u6162\u6307\u9488\u76f8\u9047 + \u6570\u5b66\u63a8\u5bfc\u5b9a\u4f4d\u5165\u53e3<\/strong>\n<ul class=\"wp-block-list\">\n<li>\u7b2c\u4e00\u6b65\uff1a\u4f7f\u7528<strong>Floyd \u5224\u5708\u7b97\u6cd5<\/strong>\uff08\u5feb\u6162\u6307\u9488\uff09\u5224\u65ad\u662f\u5426\u6709\u73af\u3002<\/li>\n\n\n\n<li>\u7b2c\u4e8c\u6b65\uff1a\u82e5\u5b58\u5728\u73af\uff0c\u5229\u7528<strong>\u8ddd\u79bb\u5173\u7cfb<\/strong>\u627e\u5230\u73af\u7684\u5165\u53e3\u8282\u70b9\u3002<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>\u6570\u5b66\u63a8\u5bfc\uff08\u5173\u952e\uff01\uff09<\/strong>\u00a0\u8bbe\uff1a<ul><li><code>a<\/code>\uff1a\u4ece\u5934\u8282\u70b9\u5230\u73af\u5165\u53e3\u7684\u8ddd\u79bb\u3002<code>b<\/code>\uff1a\u4ece\u73af\u5165\u53e3\u5230\u5feb\u6162\u6307\u9488<strong>\u7b2c\u4e00\u6b21\u76f8\u9047\u70b9<\/strong>\u7684\u8ddd\u79bb\u3002<code>c<\/code>\uff1a\u4ece\u76f8\u9047\u70b9\u7ed5\u73af\u56de\u5230\u5165\u53e3\u7684\u8ddd\u79bb\uff08\u5373\u73af\u5269\u4f59\u90e8\u5206\uff09\u3002\u73af\u603b\u957f\uff1a<code>b + c<\/code>\u3002<\/li><\/ul>\u5f53\u5feb\u6162\u6307\u9488\u76f8\u9047\u65f6\uff1a<ul><li><code>slow<\/code>\u00a0\u8d70\u4e86\uff1a<code>a + b fast<\/code>\u00a0\u8d70\u4e86\uff1a<code>a + b + c + b = a + 2b + c<\/code>\uff08\u56e0\u4e3a\u00a0<code>fast<\/code>\u00a0\u53ef\u80fd\u7ed5\u73af\u591a\u8d70\u4e86\u4e00\u5708\uff09<\/li><\/ul>\u7531\u4e8e <code>fast<\/code> \u901f\u5ea6\u662f <code>slow<\/code> \u7684 2 \u500d\uff1a<code>2(a + b) = a + 2b + c => 2a + 2b = a + 2b + c => a = c<\/code>\u7ed3\u8bba\uff1a\u4ece\u5934\u8282\u70b9\u5230\u73af\u5165\u53e3\u7684\u8ddd\u79bb <code>a<\/code>\uff0c\u7b49\u4e8e\u4ece\u76f8\u9047\u70b9\u5230\u73af\u5165\u53e3\u7684\u8ddd\u79bb <code>c<\/code>\uff01<\/li>\n\n\n\n<li><strong>\u5982\u4f55\u5229\u7528 a = c \u627e\u5230\u5165\u53e3\uff1f<\/strong><ul><li>\u5c06\u00a0<code>slow<\/code>\u00a0\u6307\u9488<strong>\u91cd\u7f6e\u5230\u5934\u8282\u70b9\u00a0<code>head<\/code><\/strong>\u3002<\/li><li><code>fast<\/code>\u00a0\u6307\u9488\u4fdd\u6301\u5728<strong>\u76f8\u9047\u70b9<\/strong>\u3002<\/li><li>\u4e24\u4e2a\u6307\u9488\u90fd<strong>\u6bcf\u6b21\u8d70\u4e00\u6b65<\/strong>\u3002<\/li><li>\u5f53\u5b83\u4eec\u518d\u6b21\u76f8\u9047\u65f6\uff0c\u76f8\u9047\u70b9\u5c31\u662f<strong>\u73af\u7684\u5165\u53e3<\/strong>\u3002<\/li><\/ul>\u56e0\u4e3a\uff1a\n<ul class=\"wp-block-list\">\n<li><code>slow<\/code>\u00a0\u4ece\u5934\u8d70\u00a0<code>a<\/code>\u00a0\u6b65 \u2192 \u5230\u8fbe\u5165\u53e3\u3002<\/li>\n\n\n\n<li><code>fast<\/code>\u00a0\u4ece\u76f8\u9047\u70b9\u8d70\u00a0<code>c<\/code>\u00a0\u6b65 \u2192 \u4e5f\u5230\u8fbe\u5165\u53e3\uff08\u56e0\u4e3a\u00a0<code>a = c<\/code>\uff09\u3002<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>\u4e3e\u4f8b\u8bf4\u660e<\/strong>\uff1a\u00a0\u5bf9 <code>head = [3,2,0,-4]<\/code>\uff0c\u73af\u8fde\u63a5\u5230 <code>2<\/code>\uff08\u7d22\u5f15 1\uff09\uff1a\n<ul class=\"wp-block-list\">\n<li>\u7b2c\u4e00\u9636\u6bb5\uff1a<code>fast<\/code>\u00a0\u548c\u00a0<code>slow<\/code>\u00a0\u5728\u00a0<code>-4<\/code>\u00a0\u5904\u76f8\u9047\uff08\u5047\u8bbe\uff09\u3002<\/li>\n\n\n\n<li><code>a = 1<\/code>\uff08<code>3 \u2192 2<\/code>\uff09<\/li>\n\n\n\n<li><code>b = 2<\/code>\uff08<code>2 \u2192 0 \u2192 -4<\/code>\uff09<\/li>\n\n\n\n<li><code>c = 1<\/code>\uff08<code>-4 \u2192 2<\/code>\uff09<\/li>\n\n\n\n<li>\u63a8\u5bfc\u5f97\u00a0<code>a = c = 1<\/code>\u3002<\/li>\n\n\n\n<li><code>slow<\/code>\u00a0\u4ece\u00a0<code>3<\/code>\u00a0\u51fa\u53d1\uff0c<code>fast<\/code>\u00a0\u4ece\u00a0<code>-4<\/code>\u00a0\u51fa\u53d1\uff0c\u5404\u8d70 1 \u6b65\uff1a\n<ul class=\"wp-block-list\">\n<li><code>slow<\/code>\u00a0\u5230\u00a0<code>2<\/code>\uff0c<code>fast<\/code>\u00a0\u5230\u00a0<code>2<\/code>\u00a0\u2192 \u76f8\u9047\uff01\u8fd4\u56de\u00a0<code>2<\/code>\u00a0\u2705<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>\u8fb9\u754c\u5904\u7406<\/strong>\uff1a\n<ul class=\"wp-block-list\">\n<li>\u7a7a\u94fe\u8868\uff1a<code>fast == null<\/code>\u00a0\u2192 \u8fd4\u56de\u00a0<code>null<\/code>\u3002<\/li>\n\n\n\n<li>\u5355\u8282\u70b9\u6709\u73af\uff1a<code>head.next = head<\/code>\u00a0\u2192 \u7b2c\u4e00\u9636\u6bb5\u00a0<code>fast == slow<\/code>\u00a0\u2192\u00a0<code>slow = head<\/code>\u00a0\u2192\u00a0<code>while(slow != fast)<\/code>\u00a0\u4e0d\u6267\u884c \u2192 \u8fd4\u56de\u00a0<code>head<\/code>\u00a0\u2705<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"<p>\ud83d\udd17 \u73af\u5f62\u94fe\u8868 II\uff1a\u5bfb\u627e\u73af\u7684\u5165\u53e3 \u9898\u76ee\u6765\u6e90\uff1a142. \u73af\u5f62\u94fe\u8868 II &#8211; \u529b\u6263\uff08LeetCode\uff09 [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[12,38],"tags":[16,14,51],"class_list":["post-369","post","type-post","status-publish","format-standard","hentry","category-algorithm","category-linked_list","tag-double_pointers","tag-algorithm","tag-linked_list"],"_links":{"self":[{"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/posts\/369","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/comments?post=369"}],"version-history":[{"count":1,"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/posts\/369\/revisions"}],"predecessor-version":[{"id":373,"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/posts\/369\/revisions\/373"}],"wp:attachment":[{"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/media?parent=369"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/categories?post=369"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/tags?post=369"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}