{"id":912,"date":"2025-10-26T16:25:01","date_gmt":"2025-10-26T08:25:01","guid":{"rendered":"https:\/\/www.guanhaobo.cn\/?p=912"},"modified":"2025-10-26T16:25:01","modified_gmt":"2025-10-26T08:25:01","slug":"leetcode-142-%e7%8e%af%e5%bd%a2%e9%93%be%e8%a1%a8-ii","status":"publish","type":"post","link":"https:\/\/www.guanhaobo.cn\/?p=912","title":{"rendered":"LeetCode 142 \u2013 \u73af\u5f62\u94fe\u8868 II"},"content":{"rendered":"

\u9898\u76ee\u63cf\u8ff0<\/h1>\n

\u7ed9\u5b9a\u4e00\u4e2a\u94fe\u8868\u7684\u5934\u8282\u70b9 head \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 null\u3002<\/p>\n

\u5982\u679c\u94fe\u8868\u4e2d\u6709\u67d0\u4e2a\u8282\u70b9\uff0c\u53ef\u4ee5\u901a\u8fc7\u8fde\u7eed\u8ddf\u8e2a next \u6307\u9488\u518d\u6b21\u5230\u8fbe\uff0c\u5219\u94fe\u8868\u4e2d\u5b58\u5728\u73af\u3002 \u4e3a\u4e86\u8868\u793a\u7ed9\u5b9a\u94fe\u8868\u4e2d\u7684\u73af\uff0c\u8bc4\u6d4b\u7cfb\u7edf\u5185\u90e8\u4f7f\u7528\u6574\u6570 pos \u6765\u8868\u793a\u94fe\u8868\u5c3e\u8fde\u63a5\u5230\u94fe\u8868\u4e2d\u7684\u4f4d\u7f6e\uff08\u7d22\u5f15\u4ece 0 \u5f00\u59cb\uff09\u3002\u5982\u679c pos \u662f -1\uff0c\u5219\u5728\u8be5\u94fe\u8868\u4e2d\u6ca1\u6709\u73af\u3002\u6ce8\u610f\uff1apos \u4e0d\u4f5c\u4e3a\u53c2\u6570\u8fdb\u884c\u4f20\u9012\uff0c\u4ec5\u4ec5\u662f\u4e3a\u4e86\u6807\u8bc6\u94fe\u8868\u7684\u5b9e\u9645\u60c5\u51b5\u3002<\/p>\n

\u4e0d\u5141\u8bb8\u4fee\u6539 \u94fe\u8868\u3002<\/p>\n

\u793a\u4f8b1
\n\"\"<\/a>
\n\u8f93\u5165\uff1ahead = [3,2,0,-4], pos = 1
\n\u8f93\u51fa\uff1a\u8fd4\u56de\u7d22\u5f15\u4e3a 1 \u7684\u94fe\u8868\u8282\u70b9
\n\u89e3\u91ca\uff1a\u94fe\u8868\u4e2d\u6709\u4e00\u4e2a\u73af\uff0c\u5176\u5c3e\u90e8\u8fde\u63a5\u5230\u7b2c\u4e8c\u4e2a\u8282\u70b9\u3002<\/p>\n

\u9898\u76ee\u5206\u6790<\/h1>\n

\u5feb\u6162\u6307\u9488\uff0c\u5206\u522b\u6bcf\u6b21\u8d702\u6b65\u548c1\u6b65\uff0c\u7b2c\u4e00\u6b21\u76f8\u9047\u65f6\u505c\u6b62\u3002
\n\u4e24\u4e2a\u6307\u9488\u4e4b\u6240\u4ee5\u4f1a\u76f8\u9047\uff0c\u662f\u56e0\u4e3a\u5feb\u6307\u9488\u6bd4\u6162\u6307\u9488\u591a\u8d70\u4e86\u4e00\u4e2a\u73af\u7684\u5468\u957f\u3002
\n\u7531\u4e8e\u5feb\u6307\u9488\u8d70\u7684\u957f\u5ea6\u662f\u6162\u6307\u94882\u500d\uff0c\u6240\u4ee5\u6162\u6307\u9488\u8d70\u7684\u957f\u5ea6\u7b49\u4e8e\u73af\u7684\u5468\u957f\u3002
\n\u5982\u56fe\u6240\u793a\uff0c\u5047\u8bbe\u7d2b\u8272\u70b9\u4e3a\u5feb\u6162\u6307\u9488\u76f8\u9047\u70b9\uff1a
\n– \u6162\u6307\u9488\u7684\u6b65\u6570\uff1aa + b
\n– \u5feb\u6307\u9488\u7684\u6b65\u6570\uff1a2 * (a + b)
\n– \u5feb\u6307\u9488\u591a\u8d70\u4e86\u4e00\u4e2a\u73af\u7684\u5468\u957f\uff1a b + c<\/p>\n

\u7efc\u5408\u53ef\u5f97 a + b = b + c\uff0c\u5373 a = c
\n\"\"<\/a>
\n\u6b64\u65f6\u8ba9\u5feb\u6307\u9488\u4ece\u5934\u5f00\u59cb\u8d70\uff0c\u6bcf\u6b211\u6b65\uff0c\u4e0e\u6162\u6307\u9488\u518d\u6b21\u76f8\u9047\u65f6\uff0c\u5373\u4e3a\u73af\u7684\u8d77\u59cb\u70b9\u3002
\n\u7a7a\u95f4\u590d\u6742\u5ea6 O(1)<\/p>\n

Java<\/h1>\n
public ListNode detectCycle(ListNode head) {\n    ListNode slow = head, fast = head;\n    if (head == null || head.next == null) {\n        return null;\n    }\n    do {\n        slow = slow.next;\n        fast = fast.next.next;\n    } while (fast != null && fast.next != null && slow != fast);\n    if (fast == null || slow != fast) {\n        return null;\n    }\n    fast = head;\n    while (slow != fast) {\n        slow = slow.next;\n        fast = fast.next;\n    }\n    return slow;\n}\n<\/code><\/pre>\n
Kotlin<\/h1>\n
fun detectCycle(head: ListNode?): ListNode? {\n    var slow = head\n    var fast = head\n    do {\n        slow = slow?.next\n        fast = fast?.next?.next\n    } while (fast?.next != null && slow != fast)\n    if (fast == null || slow != fast) {\n        return null\n    }\n    fast = head\n    while (fast != slow) {\n        slow = slow?.next\n        fast = fast?.next\n    }\n    return fast\n}\n<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
\u9898\u76ee\u63cf\u8ff0 \u7ed9\u5b9a\u4e00\u4e2a\u94fe\u8868\u7684\u5934\u8282\u70b9 head \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 null\u3002  […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[20,75,82,84],"class_list":["post-912","post","type-post","status-publish","format-standard","hentry","category-algo","tag-leetcode","tag-75","tag-82","tag-84"],"_links":{"self":[{"href":"https:\/\/www.guanhaobo.cn\/index.php?rest_route=\/wp\/v2\/posts\/912","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.guanhaobo.cn\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.guanhaobo.cn\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.guanhaobo.cn\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.guanhaobo.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=912"}],"version-history":[{"count":1,"href":"https:\/\/www.guanhaobo.cn\/index.php?rest_route=\/wp\/v2\/posts\/912\/revisions"}],"predecessor-version":[{"id":913,"href":"https:\/\/www.guanhaobo.cn\/index.php?rest_route=\/wp\/v2\/posts\/912\/revisions\/913"}],"wp:attachment":[{"href":"https:\/\/www.guanhaobo.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=912"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.guanhaobo.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=912"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.guanhaobo.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=912"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}