LeetCode: Binary Tree Traversal 题目:树的先序和后序. 后序地址:https://oj.leetcode.com/problems/binary-tree-postorder-traversal/ 先序地址:https://oj.leetcode.com/problems/binary-tree-preorder-traversal/ 后序算法:利用栈的非递归算法.初始时,先从根节点一直往左走到底,并把相应的元素进栈:在循环里每次都取出栈顶元素,如果该栈顶元素的右…

1.Preorder Traversal Given a binary tree, return the preorder traversal of its nodes' values. For example:Given binary tree {1,#,2,3}, 1 \ 2 / 3 return [1,2,3]. Note: Recursive solution is trivial, could you do it iteratively? 解题:前序遍历首先访问根结点然后遍历左子树,最…

把三个二叉树遍历的题放在一起了. 递归写法太简单,就不再实现了,每题实现了两种非递归算法. 一种是利用栈,时间和空间复杂度都是O(n). 另一种是借助线索二叉树,也叫Morris遍历,充分利用树中节点的空指针域. 先序: Binary Tree Preorder Traversal Given a binary tree, return the preorder traversal of its nodes' values. For example:Given binary tree {1,#,…

［抄题］:二叉树前序遍历 ［思维问题］: 不会递归.三要素:下定义.拆分问题(eg root-root.left).终止条件 ［一句话思路］: 节点非空时往左移,否则新取一个点 再往右移. ［输入量］:空: 正常情况:特大:特小:程序里处理到的特殊情况:异常情况(不合法不合理的输入): ［画图］: ［一刷］: 不要提起加入root节点. ［二刷］: ［三刷］: ［四刷］: ［五刷］: ［总结］: ［复杂度］:Time complexity: O(n) Space complexity: O(n)…

二叉树的递归遍历比较简单,这里说一下非递归遍历,以中序遍历为例子. 非递归遍历主要用到栈来协助进行.对于一个二叉树,首先根节点入栈,如果有左儿子,则继续入栈,重复直到最左边的儿子,这时候此节点值为要遍历的第一个值,他父亲是在栈顶.所以我们做一次出栈操作   f = stack.pop(),并将 f.val 值存为第二个点,接下来要遍历 f.right,完成后栈的最后元素是  f  的父亲,继续做出栈操作.重复下去可以完成遍历. def inorderTraversal(self, root):…

Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and alternate between). For example:Given binary tree {3,9,20,#,#,15,7}, 3 / \ 9 20 / \ 15 7 return its…

Sept. 13, 2015 Spent more than a few hours to work on the leetcode problem, and my favorite blogs about this problems: 1. http://siddontang.gitbooks.io/leetcode-solution/content/tree/construct_binary_tree.html 2.http://blog.csdn.net/linhuanmars/artic…

Given a binary tree, return the vertical order traversal of its nodes' values. (ie, from top to bottom, column by column). If two nodes are in the same row and column, the order should be from left to right. Examples: Given binary tree [3,9,20,null,n…

Given a binary tree, return the postorder traversal of its nodes' values. For example: Given binary tree {1,#,2,3}, 1 \ 2 / 3 return [3,2,1]. Note: Recursive solution is trivial, could you do it iteratively? 经典题目,求二叉树的后序遍历的非递归方法,跟前序,中序,层序一样都需要用到栈,后续的…

Given a binary tree, return the preorder traversal of its nodes' values. For example:Given binary tree {1,#,2,3}, 1 \ 2 / 3 return [1,2,3]. Note: Recursive solution is trivial, could you do it iteratively? 一般我们提到树的遍历,最常见的有先序遍历,中序遍历,后序遍历和层序遍历,它们用递归实现起…