{"id":555,"date":"2025-07-03T08:17:03","date_gmt":"2025-07-03T00:17:03","guid":{"rendered":"https:\/\/189505.xyz\/?p=555"},"modified":"2025-08-05T10:01:40","modified_gmt":"2025-08-05T02:01:40","slug":"leetcode","status":"publish","type":"post","link":"https:\/\/189505.xyz\/?p=555","title":{"rendered":"leetcode"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_40 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" area-label=\"ez-toc-toggle-icon-1\"><label for=\"item-69e031e74bc0a\" aria-label=\"Table of Content\"><span style=\"display: flex;align-items: center;width: 35px;height: 30px;justify-content: center;direction:ltr;\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/label><input  type=\"checkbox\" id=\"item-69e031e74bc0a\"><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/189505.xyz\/?p=555\/#Leetcode_454_4Sum_II\" title=\"Leetcode 454. 4Sum II\">Leetcode 454. 4Sum II<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/189505.xyz\/?p=555\/#lc142_Linked_List_Cycle_II\" title=\"lc142 Linked List Cycle II\">lc142 Linked List Cycle II<\/a><ul class='ez-toc-list-level-2'><li class='ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/189505.xyz\/?p=555\/#%E5%BF%AB%E6%8C%87%E9%92%88%E4%BB%BB%E4%BD%95%E6%97%B6%E5%80%99%E8%B5%B0%E7%9A%84%E8%B7%9D%E7%A6%BB%E4%B8%80%E5%AE%9A%E4%B8%BA%E6%85%A2%E6%8C%87%E9%92%88%E7%9A%84_2_%E5%80%8D\" title=\"\u5feb\u6307\u9488\u4efb\u4f55\u65f6\u5019\u8d70\u7684\u8ddd\u79bb\u4e00\u5b9a\u4e3a\u6162\u6307\u9488\u7684 2 \u500d\">\u5feb\u6307\u9488\u4efb\u4f55\u65f6\u5019\u8d70\u7684\u8ddd\u79bb\u4e00\u5b9a\u4e3a\u6162\u6307\u9488\u7684 2 \u500d<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/189505.xyz\/?p=555\/#%E4%B8%BA%E4%BB%80%E4%B9%88%E5%BF%AB%E6%85%A2%E6%8C%87%E9%92%88%E7%9B%B8%E9%81%87%E6%97%B6%E6%85%A2%E6%8C%87%E9%92%88%E6%B2%A1%E6%9C%89%E8%B5%B0%E5%AE%8C%E4%B8%80%E5%9C%88\" title=\"\u4e3a\u4ec0\u4e48\u5feb\u6162\u6307\u9488\u76f8\u9047\u65f6\u6162\u6307\u9488\u6ca1\u6709\u8d70\u5b8c\u4e00\u5708\">\u4e3a\u4ec0\u4e48\u5feb\u6162\u6307\u9488\u76f8\u9047\u65f6\u6162\u6307\u9488\u6ca1\u6709\u8d70\u5b8c\u4e00\u5708<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/189505.xyz\/?p=555\/#%E5%88%A9%E7%94%A8%E7%AC%AC%E4%B8%89%E4%B8%AA%E6%8C%87%E9%92%88%E6%89%BE%E5%88%B0%E7%8E%AF%E7%9A%84%E4%BD%8D%E7%BD%AE\" title=\"\u5229\u7528\u7b2c\u4e09\u4e2a\u6307\u9488\u627e\u5230\u73af\u7684\u4f4d\u7f6e\">\u5229\u7528\u7b2c\u4e09\u4e2a\u6307\u9488\u627e\u5230\u73af\u7684\u4f4d\u7f6e<\/a><\/li><\/ul><\/li><\/ul><\/nav><\/div>\n<h1><span class=\"ez-toc-section\" id=\"Leetcode_454_4Sum_II\"><\/span>Leetcode 454. 4Sum II<span class=\"ez-toc-section-end\"><\/span><\/h1>\n<p><a href=\"https:\/\/leetcode.jp\/leetcode-454-4sum-ii-%E8%A7%A3%E9%A2%98%E6%80%9D%E8%B7%AF%E5%88%86%E6%9E%90\/\">https:\/\/leetcode.jp\/leetcode-454-4sum-ii-%E8%A7%A3%E9%A2%98%E6%80%9D%E8%B7%AF%E5%88%86%E6%9E%90\/<\/a><br \/>\n\u6458\u8981:<br \/>\n\u4e2a\u4eba\u8ba4\u4e3a\u672c\u9898\u4e0eTwo Sum\u5c5e\u4e8e\u540c\u7c7b\u578b\u9898\u76ee\uff0c\u4e3b\u8981\u8003\u5bdfHashMap\uff0c\u800c3Sum\u4e0e4Sum\u53c8\u662f\u53e6\u5916\u4e00\u4e2a\u7c7b\u578b\uff0c\u5747\u53ef\u4f7f\u7528\u53cc\u6307\u9488\u601d\u8def\u6765\u89e3\u9898\u3002<\/p>\n<p>\u5206\u6790\u672c\u9898\u4e4b\u524d\uff0c\u6211\u89c9\u5f97\u6709\u5fc5\u8981\u8bf4\u4e0b\u672c\u9898\u4e0e\u524d\u4e00\u96c64Sum\u7684\u533a\u522b\uff0c\u867d\u7136\u90fd\u662f\u6c424\u4e2a\u6570\u548c\u4e3a\u67d0\u4e2aTarget\u7684\u9898\u76ee\uff0c\u4f46\u662f\u533a\u522b\u5728\u4e8e\uff0c\u672c\u9898\u662f\u57284\u4e2a\u6570\u7ec4\u4e2d\u5206\u522b\u627e4\u4e2a\u6570\u5b57\uff0c\u524d\u4e00\u9898\u5219\u662f\u5728\u4e00\u4e2a\u6570\u7ec4\u4e2d\u627e\u3002\u6211\u4eec\u8981\u660e\u767d\u4ed6\u4eec\u5728\u672c\u8d28\u4e0a\u7684\u4e0d\u540c\uff0c\u624d\u80fd\u7406\u89e3\u4e3a\u4ec0\u4e48\u4e0d\u80fd\u4f7f\u7528\u540c\u4e00\u79cd\u89e3\u9898\u65b9\u6cd5\u3002\u5f53\u5728\u4e00\u4e2a\u6570\u7ec4\u4e2d\u627e4\u4e2a\u6570\u5b57\u65f6\uff0c\u6211\u4eec\u89e3\u6cd5\u4f7f\u7528\u7684\u65f6\u95f4\u590d\u6742\u5ea6\u4e3aO(n^3)\uff0c\u524d\u4e24\u5c42\u5faa\u73af\u662f\u5728\u627e\u524d\u4e24\u4e2a\u6570\uff0c\u7b2c\u4e09\u5c42\u5faa\u73af\u4f7f\u7528\u53cc\u6307\u9488\u6765\u627e\u540e\u4e24\u4e2a\u6570\u3002\u5176\u5b9e\u672c\u9898\u4e5f\u80fd\u4f7f\u7528\u8be5\u65b9\u6cd5\uff0c\u4f46\u662f\u96be\u70b9\u5728\u4e8e\u65e0\u6cd5\u526a\u679d\uff014Sum\u867d\u7136\u4f7f\u7528\u4e86O(n^3)\u7684\u65f6\u95f4\u590d\u6742\u5ea6\uff0c\u4f46\u662f\u526a\u679d\u64cd\u4f5c\u8ba9\u5176\u6267\u884c\u6b21\u6570\u8fdc\u8fdc\u5c0f\u4e8en\u7684\u4e09\u6b21\u65b9\uff0c\u526a\u679d\u7684\u6838\u5fc3\u5728\u4e8e\uff0c\u56e0\u4e3a\u53ea\u6709\u4e00\u4e2a\u6570\u7ec4\uff0c\u5f53\u5b83\u6392\u5e8f\u4e4b\u540e\uff0c\u5982\u679c\u5f53\u524d\u6570\u5df2\u7ecf\u5927\u4e8eTarget\uff0c\u90a3\u4e48\u5728\u5b83\u540e\u9762\u7684\u5176\u4ed6\u6570\u5b57\u80af\u5b9a\u4e5f\u90fd\u5927\u4e8eTarget\uff0c\u6b64\u65f6\u53ef\u4ee5\u7ed3\u675f\u5faa\u73af\u3002\u800c\u56de\u5230\u672c\u9898\uff0c\u6211\u4eec\u9700\u8981\u57284\u4e2a\u6570\u7ec4\u4e2d\u5206\u522b\u6311\u4e00\u4e2a\u6570\u51fa\u6765\uff0c\u8fd9\u6837\uff0c\u5373\u4f7f\u5f53\u524d\u6570\u5b57\u5927\u4e8eTarget\uff0c\u6211\u4eec\u4e5f\u4e0d\u80fd\u786e\u5b9a\u5176\u4ed6\u6570\u7ec4\u4e2d\u6311\u51fa\u7684\u6570\u5b57\u662f\u5426\u4e5f\u90fd\u5927\u4e8eTarget\uff0c\u8fd9\u6837\u4e00\u6765\uff0c\u5c31\u6ca1\u6709\u529e\u6cd5\u8fdb\u884c\u526a\u679d\u64cd\u4f5c\u4e86\u3002<\/p>\n<p>\u90a3\u4e48\u672c\u9898\u8be5\u5982\u4f55\u89e3\u5462\uff1f\u4e0a\u6587\u5df2\u7ecf\u8bf4\u8fc7\uff0c\u672c\u9898\u5176\u5b9e\u4e0eTwo Sum\u5f88\u76f8\u4f3c\uff0c\u6211\u4eec\u5c064\u4e2a\u6570\u7ec4\u5206\u62102\u7ec4\uff0cA\uff0cB\u548cC\uff0cD\uff0c\u5148\u4f7f\u7528\u4e24\u5c42\u5faa\u73af\u904d\u5386A\u548cB\u4e2d\u6240\u6709\u5143\u7d20\u4e24\u4e24\u4e4b\u548c\uff0c\u5e76\u5c06\u7ed3\u679c\u4fdd\u5b58\u81f3HashMap\uff0c\u5176\u4e2dkey\u4e3a\u4e24\u5143\u7d20\u4e4b\u548c\uff0cvalue\u4e3a\u8be5\u548c\u51fa\u73b0\u7684\u6b21\u6570\u3002\u4e4b\u540e\u518d\u4f7f\u7528\u4e24\u5c42\u5faa\u73af\u904d\u5386C\u548cD\u4e2d\u6240\u6709\u5143\u7d20\u4e24\u4e24\u4e4b\u548c\uff0c\u5e76\u67e5\u770b\u8be5\u548c\u7684\u76f8\u53cd\u6570\u5728map\u4e2d\u5b58\u5728\u7684\u4e2a\u6570\uff0c\u5e76\u5c06\u4e2a\u6570\u7d2f\u52a0\u81f3\u8fd4\u56de\u7ed3\u679c\u5373\u53ef\u3002<\/p>\n<h1><span class=\"ez-toc-section\" id=\"lc142_Linked_List_Cycle_II\"><\/span>lc142 Linked List Cycle II<span class=\"ez-toc-section-end\"><\/span><\/h1>\n<h2><span class=\"ez-toc-section\" id=\"%E5%BF%AB%E6%8C%87%E9%92%88%E4%BB%BB%E4%BD%95%E6%97%B6%E5%80%99%E8%B5%B0%E7%9A%84%E8%B7%9D%E7%A6%BB%E4%B8%80%E5%AE%9A%E4%B8%BA%E6%85%A2%E6%8C%87%E9%92%88%E7%9A%84_2_%E5%80%8D\"><\/span>\u5feb\u6307\u9488\u4efb\u4f55\u65f6\u5019\u8d70\u7684\u8ddd\u79bb\u4e00\u5b9a\u4e3a\u6162\u6307\u9488\u7684 2 \u500d<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>fast \u6307\u9488\u5728\u4efb\u4f55\u65f6\u5019\u8d70\u7684\u8ddd\u79bb\u4e00\u5b9a\u662f slow \u6307\u9488\u7684 2 \u500d\uff0c\u8fd9\u4e2a\u7ed3\u8bba\u6211\u60f3\u5927\u5bb6\u90fd\u6ca1\u4ec0\u4e48\u7591\u95ee\uff0c\u77e5\u9053\u4e86\u8fd9\u4e2a\u7ed3\u8bba\u4e4b\u540e\uff0c\u6211\u4eec\u518d\u6765\u770b\u4e00\u4e0b\u4e0b\u9762\u8fd9\u5e45\u56fe\uff1a<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/static.189505.xyz\/blogImages\/leetcode\/double-pointer.png\"><\/p>\n<p>\u4e0a\u56fe\u4e2d\u4ee5\u8282\u70b9\u4e3a\u5212\u5206\uff0c\u6709\u4e09\u6bb5\u94fe\u8868\uff0ca\uff0cb\uff0cc \u5206\u522b\u8868\u793a\u4e09\u6bb5\u7684\u8ddd\u79bb\uff0c\u6211\u4eec\u5047\u8bbe\u5f53\u5feb\u6162\u6307\u9488\u76f8\u9047\u7684\u65f6\u5019\uff0c\u5feb\u6307\u9488\u5df2\u7ecf\u5728\u73af\u4e2d\u8d70\u4e86 n \u5708\uff0c\u90a3\u4e48\u5c31\u53ef\u4ee5\u5f97\u5230\u5feb\u6307\u9488\u8d70\u8fc7\u7684\u8ddd\u79bb\u4e3a\uff1aa+n*(b+c)+b\uff0c\u800c\u6162\u6307\u9488\u8d70\u8fc7\u7684\u8ddd\u79bb\u4e3a a+b\uff0c\u6839\u636e\u5feb\u6307\u9488\u8d70\u7684\u8def\u7a0b\u4e00\u5b9a\u662f\u6162\u6307\u9488\u7684\u4e24\u500d\uff0c\u53ef\u4ee5\u5f97\u5230\u5982\u4e0b\u7b49\u5f0f\uff1a<\/p>\n<p>a+n<em>(b+c)+b = 2<\/em>(a+b)\uff0c\u6700\u7ec8\u7ecf\u8fc7\u8f6c\u6362\uff0c\u5f97\u5230 a=(n-1)*(b+c) + c\u3002<\/p>\n<p>\u5230\u8fd9\u91cc\u53ef\u80fd\u6709\u4eba\u4f1a\u6709\u7591\u95ee\uff0c\u5feb\u6162\u6307\u9488\u76f8\u9047\u7684\u65f6\u5019\uff0c\u4e3a\u4ec0\u4e48\u6162\u6307\u9488\u4e00\u5b9a\u6ca1\u6709\u8d70\u5b8c\u4e00\u5708\u5462\uff1f\u5982\u679c\u6162\u6307\u9488\u4e5f\u8d70\u4e86 m \u5708\uff0c\u90a3\u4e48\u6162\u6307\u9488\u8d70\u8fc7\u7684\u8ddd\u79bb\u5c31\u662f a+m*(b+c)+b \u4e86\uff0c\u4f46\u662f\u8fd9\u5176\u5b9e\u662f\u4e0d\u53ef\u80fd\u7684\u3002<\/p>\n<h2><span class=\"ez-toc-section\" id=\"%E4%B8%BA%E4%BB%80%E4%B9%88%E5%BF%AB%E6%85%A2%E6%8C%87%E9%92%88%E7%9B%B8%E9%81%87%E6%97%B6%E6%85%A2%E6%8C%87%E9%92%88%E6%B2%A1%E6%9C%89%E8%B5%B0%E5%AE%8C%E4%B8%80%E5%9C%88\"><\/span>\u4e3a\u4ec0\u4e48\u5feb\u6162\u6307\u9488\u76f8\u9047\u65f6\u6162\u6307\u9488\u6ca1\u6709\u8d70\u5b8c\u4e00\u5708<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>\u6211\u4eec\u5047\u8bbe\u8fd9\u4e2a\u73af\u7684\u957f\u5ea6\u4e3a x\uff0c\u90a3\u4e48\u5f53 slow \u6307\u9488\u8d70\u5b8c\u4e00\u5708\u65f6\uff0c\u9700\u8981\u8d70 x \u6b65\uff0c\u800c\u5f53 slow \u6307\u9488\u8d70\u5b8c x \u6b65\uff0cfast \u6307\u9488\u5df2\u7ecf\u8d70\u4e86 2x \u6b65\u4e86\uff0c\u4e5f\u5c31\u662f\u8d70\u4e86\u4e24\u5708\u4e86\uff0c\u90a3\u4e48\u4ed6\u4eec\u4e00\u5b9a\u5728\u67d0\u4e00\u4e2a\u70b9\u76f8\u9047\u8fc7\u4e86\uff08\u56e0\u4e3a\u4ed6\u4eec\u4e0d\u53ef\u80fd\u9519\u8fc7\u76f8\u9047\u70b9\uff09\uff0c\u6240\u4ee5\u5f53\u5feb\u6162\u6307\u9488\u7b2c\u4e00\u6b21\u76f8\u9047\u65f6\uff0c\u6162\u6307\u9488\u662f\u4e0d\u53ef\u80fd\u8d70\u5b8c\u4e00\u5708\u7684\u3002<\/p>\n<h2><span class=\"ez-toc-section\" id=\"%E5%88%A9%E7%94%A8%E7%AC%AC%E4%B8%89%E4%B8%AA%E6%8C%87%E9%92%88%E6%89%BE%E5%88%B0%E7%8E%AF%E7%9A%84%E4%BD%8D%E7%BD%AE\"><\/span>\u5229\u7528\u7b2c\u4e09\u4e2a\u6307\u9488\u627e\u5230\u73af\u7684\u4f4d\u7f6e<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>\u7ee7\u7eed\u56de\u5230\u4e0a\u9762\u7684\u7b49\u5f0f\uff1aa=(n-1)*(b+c) + c\uff0c\u7136\u540e\u6211\u4eec\u53ef\u4ee5\u53d1\u73b0\uff0c\u5176\u5b9e b+c \u6b63\u597d\u7b49\u4e8e\u73af\u7684\u957f\u5ea6\uff0c\u4e5f\u5c31\u662f\u8bf4\uff1a\u4ece\u94fe\u8868\u5934\u90e8\u5230\u5165\u73af\u7684\u8ddd\u79bb\uff08a\uff09\u6070\u597d\u7b49\u4e8e\u4ece\u76f8\u9047\u70b9\u5230\u5165\u73af\u70b9\u7684\u8ddd\u79bb\uff08c\uff09\u518d\u52a0\u4e0a n-1 \u5708\u4e2a\u73af\u7684\u957f\u5ea6\u3002<\/p>\n<p>\u8fd9\u65f6\u5019\u5c31\u6709\u4e2a\u6709\u8da3\u7684\u73b0\u8c61\u4e86\uff0c\u5982\u679c slow \u548c fast \u76f8\u9047\u4e86\uff0c\u90a3\u4e48\u8fd9\u65f6\u5019\u6211\u4eec\u518d\u5b9a\u4e49\u4e00\u4e2a\u6307\u9488\u6307\u5411\u94fe\u8868\u8d77\u70b9\uff0c\u4e00\u6b21\u8d70\u4e00\u6b65\uff0cslow \u6307\u9488\u4e5f\u540c\u6b65\u7ee7\u7eed\u5f80\u540e\u8d70\uff0c\u90a3\u4e48\u8fd9\u4e24\u4e2a\u6307\u9488\u5c31\u4e00\u5b9a\u4f1a\u5728\u94fe\u8868\u7684\u5165\u53e3\u4f4d\u7f6e\u76f8\u9047\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Leetcode 454. 4Sum II https:\/\/leetcode.jp\/leetcode-454- &#8230; <a title=\"leetcode\" class=\"read-more\" href=\"https:\/\/189505.xyz\/?p=555\" aria-label=\"More on leetcode\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"_links":{"self":[{"href":"https:\/\/189505.xyz\/index.php?rest_route=\/wp\/v2\/posts\/555"}],"collection":[{"href":"https:\/\/189505.xyz\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/189505.xyz\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/189505.xyz\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/189505.xyz\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=555"}],"version-history":[{"count":5,"href":"https:\/\/189505.xyz\/index.php?rest_route=\/wp\/v2\/posts\/555\/revisions"}],"predecessor-version":[{"id":581,"href":"https:\/\/189505.xyz\/index.php?rest_route=\/wp\/v2\/posts\/555\/revisions\/581"}],"wp:attachment":[{"href":"https:\/\/189505.xyz\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=555"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/189505.xyz\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=555"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/189505.xyz\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=555"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}