{"id":425,"date":"2025-10-10T17:35:46","date_gmt":"2025-10-10T09:35:46","guid":{"rendered":"https:\/\/heyingnian.com\/?p=425"},"modified":"2025-10-10T17:36:27","modified_gmt":"2025-10-10T09:36:27","slug":"leetcode-102","status":"publish","type":"post","link":"https:\/\/heyingnian.com\/index.php\/2025\/10\/10\/leetcode-102\/","title":{"rendered":"\u4e8c\u53c9\u6811\u7684\u5c42\u5e8f\u904d\u5386"},"content":{"rendered":"\n<h1 class=\"wp-block-heading\">\ud83d\udd17 \u4e8c\u53c9\u6811\u7684\u5c42\u5e8f\u904d\u5386<\/h1>\n\n\n\n<p>\u9898\u76ee\u6765\u6e90\uff1a<a href=\"https:\/\/leetcode.cn\/problems\/binary-tree-level-order-traversal\/description\/?envType=study-plan-v2&amp;envId=top-100-liked\" target=\"_blank\" rel=\"noopener\">102. \u4e8c\u53c9\u6811\u7684\u5c42\u5e8f\u904d\u5386 &#8211; \u529b\u6263\uff08LeetCode\uff09<\/a><\/p>\n\n\n\n<p>\ud83d\udccc \u9898\u76ee\u63cf\u8ff0<\/p>\n\n\n\n<p>\u7ed9\u4f60\u4e8c\u53c9\u6811\u7684\u6839\u8282\u70b9 <code>root<\/code>\uff0c\u8fd4\u56de\u5176\u8282\u70b9\u503c\u7684 <strong>\u5c42\u5e8f\u904d\u5386<\/strong>\u3002<br>\uff08\u5373\u9010\u5c42\u5730\uff0c\u4ece\u5de6\u5230\u53f3\u8bbf\u95ee\u6240\u6709\u8282\u70b9\uff0c\u6bcf\u4e00\u5c42\u7684\u7ed3\u679c\u5355\u72ec\u4f5c\u4e3a\u4e00\u4e2a\u5217\u8868\u3002\uff09<\/p>\n\n\n\n<p>\u2705 \u793a\u4f8b\u89e3\u6790<\/p>\n\n\n\n<p><strong>\u793a\u4f8b 1\uff1a<\/strong><\/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\/10\/image.png'><img class=\"lazyload lazyload-style-1\" src=\"data:image\/svg+xml;base64,PCEtLUFyZ29uTG9hZGluZy0tPgo8c3ZnIHdpZHRoPSIxIiBoZWlnaHQ9IjEiIHhtbG5zPSJodHRwOi8vd3d3LnczLm9yZy8yMDAwL3N2ZyIgc3Ryb2tlPSIjZmZmZmZmMDAiPjxnPjwvZz4KPC9zdmc+\"  loading=\"lazy\" decoding=\"async\" width=\"277\" height=\"302\" data-original=\"https:\/\/heyingnian.com\/wp-content\/uploads\/2025\/10\/image.png\" src=\"data:image\/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB\/AAffA0nNPuCLAAAAAElFTkSuQmCC\" alt=\"\" class=\"wp-image-426\"  sizes=\"auto, (max-width: 277px) 100vw, 277px\" \/><\/div><\/figure>\n\n\n\n<p>\u8f93\u5165\uff1a<code>root = [3,9,20,null,null,15,7]<\/code><br>\u8f93\u51fa\uff1a<code>[[3],[9,20],[15,7]]<\/code><br>\u89e3\u91ca\uff1a<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u7b2c 0 \u5c42\uff1a<code>[3]<\/code><\/li>\n\n\n\n<li>\u7b2c 1 \u5c42\uff1a<code>[9, 20]<\/code><\/li>\n\n\n\n<li>\u7b2c 2 \u5c42\uff1a<code>[15, 7]<\/code><\/li>\n<\/ul>\n\n\n\n<p><strong>\u793a\u4f8b 2\uff1a<\/strong><\/p>\n\n\n\n<p>\u8f93\u5165\uff1a<code>root = [1]<\/code><br>\u8f93\u51fa\uff1a&#8220;<\/p>\n\n\n\n<p><strong>\u793a\u4f8b 3\uff1a<\/strong><\/p>\n\n\n\n<p>\u8f93\u5165\uff1a<code>root = []<\/code><br>\u8f93\u51fa\uff1a<code>[]<\/code><br>\u89e3\u91ca\uff1a\u7a7a\u6811\u65e0\u8282\u70b9\uff0c\u8fd4\u56de\u7a7a\u5217\u8868\u3002<\/p>\n\n\n\n<p>\u26a0\ufe0f \u63d0\u793a<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u6811\u4e2d\u8282\u70b9\u6570\u76ee\u5728\u8303\u56f4\u00a0<code>[0, 2000]<\/code>\u00a0\u5185<\/li>\n\n\n\n<li><code>-1000 &lt;= Node.val &lt;= 1000<\/code><\/li>\n<\/ul>\n\n\n\n<p>\ud83d\udca1 \u89e3\u6cd5\uff1a\u5e7f\u5ea6\u4f18\u5148\u641c\u7d22\uff08BFS\uff09 + \u961f\u5217 \u2014\u2014 O(n) \u65f6\u95f4\uff0cO(w) \u7a7a\u95f4<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>class Solution {\n    public List&lt;List&lt;Integer>> levelOrder(TreeNode root) {\n        List&lt;List&lt;Integer>> result = new ArrayList&lt;>();\n        if (root == null) {\n            return result;\n        }\n\n        Queue&lt;TreeNode> queue = new LinkedList&lt;>(); \n        queue.offer(root);\n\n        while (!queue.isEmpty()) {\n            int size = queue.size(); \/\/ \u5f53\u524d\u5c42\u7684\u8282\u70b9\u6570\u91cf\n            List&lt;Integer> currentLevel = new ArrayList&lt;>();\n\n            for (int i = 0; i &lt; size; i++) {\n                TreeNode node = queue.poll(); \n                currentLevel.add(node.val);\n\n                if (node.left != null) {\n                    queue.offer(node.left);\n                }\n                if (node.right != null) {\n                    queue.offer(node.right);\n                }\n            }\n\n            result.add(currentLevel);\n        }\n\n        return result;\n    }\n}<\/code><\/pre>\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><br>\u6bcf\u4e2a\u8282\u70b9\u6070\u597d\u5165\u961f\u548c\u51fa\u961f\u4e00\u6b21\uff0c\u603b\u64cd\u4f5c\u6b21\u6570\u4e3a O(n)\u3002<\/li>\n\n\n\n<li><strong>\u7a7a\u95f4\u590d\u6742\u5ea6\uff1aO(w)<\/strong><br><code>w<\/code> \u662f\u6811\u7684\u6700\u5927\u5bbd\u5ea6\uff08\u5373\u67d0\u4e00\u5c42\u6700\u591a\u8282\u70b9\u6570\uff09\u3002\u961f\u5217\u4e2d\u6700\u591a\u540c\u65f6\u5b58\u50a8\u4e00\u5c42\u7684\u6240\u6709\u8282\u70b9\u3002\u6700\u574f\u60c5\u51b5\u4e0b\uff08\u5b8c\u5168\u4e8c\u53c9\u6811\u6700\u540e\u4e00\u5c42\uff09\uff0c<code>w \u2248 n\/2<\/code>\uff0c\u56e0\u6b64\u7a7a\u95f4\u590d\u6742\u5ea6\u4e3a O(n)\uff1b\u4f46\u901a\u5e38\u8868\u8ff0\u4e3a O(w) \u66f4\u51c6\u786e\u3002<\/li>\n<\/ul>\n\n\n\n<p>\ud83e\udde9 \u89e3\u9898\u601d\u8def<\/p>\n\n\n\n<p><strong>\u6838\u5fc3\u601d\u60f3\uff1a\u5e7f\u5ea6\u4f18\u5148\u904d\u5386\uff08BFS\uff09<\/strong><br>\u5c42\u5e8f\u904d\u5386\u662f BFS \u5728\u4e8c\u53c9\u6811\u4e2d\u7684\u6807\u51c6\u5e94\u7528\u3002<\/p>\n\n\n\n<p><strong>\u5173\u952e\u6280\u5de7\uff1a\u6309\u5c42\u5904\u7406<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u6bcf\u6b21\u8fdb\u5165\u00a0<code>while<\/code>\u00a0\u5faa\u73af\u65f6\uff0c\u961f\u5217\u4e2d\u6070\u597d\u5305\u542b<strong>\u5f53\u524d\u5c42\u7684\u6240\u6709\u8282\u70b9<\/strong>\u3002<\/li>\n\n\n\n<li>\u901a\u8fc7\u00a0<code>int size = queue.size()<\/code>\u00a0\u56fa\u5b9a\u5f53\u524d\u5c42\u7684\u8282\u70b9\u6570\u91cf\uff0c\u786e\u4fdd\u00a0<code>for<\/code>\u00a0\u5faa\u73af\u53ea\u5904\u7406\u8fd9\u4e00\u5c42\uff0c\u907f\u514d\u4e0e\u4e0b\u4e00\u5c42\u6df7\u6dc6\u3002<\/li>\n<\/ul>\n\n\n\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>\ud83d\udd17 \u4e8c\u53c9\u6811\u7684\u5c42\u5e8f\u904d\u5386 \u9898\u76ee\u6765\u6e90\uff1a102. \u4e8c\u53c9\u6811\u7684\u5c42\u5e8f\u904d\u5386 &#8211; \u529b\u6263\uff08LeetCode\uff09 \ud83d\udccc \u9898\u76ee [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[39,12],"tags":[57,59,14],"class_list":["post-425","post","type-post","status-publish","format-standard","hentry","category-binary_tree","category-algorithm","tag-binary_tree","tag-bfs","tag-algorithm"],"_links":{"self":[{"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/posts\/425","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=425"}],"version-history":[{"count":1,"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/posts\/425\/revisions"}],"predecessor-version":[{"id":427,"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/posts\/425\/revisions\/427"}],"wp:attachment":[{"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/media?parent=425"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/categories?post=425"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/heyingnian.com\/index.php\/wp-json\/wp\/v2\/tags?post=425"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}