{"id":6168,"date":"2020-01-29T18:15:09","date_gmt":"2020-01-30T02:15:09","guid":{"rendered":"https:\/\/zxi.mytechroad.com\/blog\/?p=6168"},"modified":"2020-01-29T18:15:33","modified_gmt":"2020-01-30T02:15:33","slug":"leetcode-107-binary-tree-level-order-traversal-ii","status":"publish","type":"post","link":"https:\/\/zxi.mytechroad.com\/blog\/tree\/leetcode-107-binary-tree-level-order-traversal-ii\/","title":{"rendered":"\u82b1\u82b1\u9171 LeetCode 107. Binary Tree Level Order Traversal II"},"content":{"rendered":"\n<p>Given a binary tree, return the&nbsp;<em>bottom-up level order<\/em>&nbsp;traversal of its nodes&#8217; values. (ie, from left to right, level by level from leaf to root).<\/p>\n\n\n\n<p>For example:<br>Given binary tree&nbsp;<code>[3,9,20,null,null,15,7]<\/code>,<br><\/p>\n\n\n\n<pre class=\"wp-block-preformatted;crayon:false\">    3\n   \/ \\\n  9  20\n    \/  \\\n   15   7\n<\/pre>\n\n\n\n<p>return its bottom-up level order traversal as:<br><\/p>\n\n\n\n<pre class=\"wp-block-preformatted;crayon:false\">[\n  [15,7],\n  [9,20],\n  [3]\n]<\/pre>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>Solution: Recursion<\/strong><\/h2>\n\n\n\n<p>Time complexity: O(n)<br>Space complexity: O(n)<\/p>\n\n\n\n<div class=\"responsive-tabs\">\n<h2 class=\"tabtitle\">C++<\/h2>\n<div class=\"tabcontent\">\n\n<pre lang=\"C++\">\n\/\/ Author: Huahua\nclass Solution {\npublic:\n    vector<vector<int>> levelOrderBottom(TreeNode *root) {\n      vector<vector<int>> ans;\n      levelOrderBottom(root, 0, ans);\n      reverse(ans.begin(), ans.end());\n      return ans;\n    }\nprivate:\n    void levelOrderBottom(TreeNode *root, int depth, vector<vector<int>>& ans) {\n      if (!root) return;\n      while (ans.size() <= depth) ans.push_back({});\n      ans[depth].push_back(root->val);\n      levelOrderBottom(root->left, depth + 1, ans);\n      levelOrderBottom(root->right, depth + 1, ans);\n    }\n};\n<\/pre>\n<\/div><\/div>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>Related Problems<\/strong><\/h2>\n\n\n\n<ul class=\"wp-block-list\"><li><a href=\"https:\/\/zxi.mytechroad.com\/blog\/leetcode\/leetcode-102-binary-tree-level-order-traversal\/\">https:\/\/zxi.mytechroad.com\/blog\/leetcode\/leetcode-102-binary-tree-level-order-traversal\/<\/a><\/li><li><a href=\"https:\/\/zxi.mytechroad.com\/blog\/tree\/leetcode-429-n-ary-tree-level-order-traversal\/\">https:\/\/zxi.mytechroad.com\/blog\/tree\/leetcode-429-n-ary-tree-level-order-traversal\/<\/a><\/li><li><a href=\"https:\/\/zxi.mytechroad.com\/blog\/tree\/leetcode-872-leaf-similar-trees\/\">https:\/\/zxi.mytechroad.com\/blog\/tree\/leetcode-872-leaf-similar-trees\/<\/a><\/li><li><a href=\"https:\/\/zxi.mytechroad.com\/blog\/tree\/leetcode-987-vertical-order-traversal-of-a-binary-tree\/\">https:\/\/zxi.mytechroad.com\/blog\/tree\/leetcode-987-vertical-order-traversal-of-a-binary-tree\/<\/a><\/li><\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Given a binary tree, return the&nbsp;bottom-up level order&nbsp;traversal of its nodes&#8217; values. (ie, from left to right, level by level from leaf to root). For&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[45],"tags":[222,542,376,17,28],"class_list":["post-6168","post","type-post","status-publish","format-standard","hentry","category-tree","tag-easy","tag-level-order","tag-on","tag-recursion","tag-tree","entry","simple"],"_links":{"self":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/6168","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/comments?post=6168"}],"version-history":[{"count":2,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/6168\/revisions"}],"predecessor-version":[{"id":6170,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/6168\/revisions\/6170"}],"wp:attachment":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/media?parent=6168"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/categories?post=6168"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/tags?post=6168"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}