问题描述: Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). For example, this binary tree is symmetric: 1 / \ 2 2 / \ / \ 3 4 4 3 But the following is not: 1 / \ 2 2 \ \ 3 3 Note:Bonus points if you could solv…

题目: Two elements of a binary search tree (BST) are swapped by mistake. Recover the tree without changing its structure. Note: A solution using O(n) space is pretty straight forward. Could you devise a constant space solution? 题解: 解决方法是利用中序遍历找顺序不对的两个点…

题目: Given a binary tree, determine if it is a valid binary search tree (BST). Assume a BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node's key. The right subtree of a node contains only nodes with…

题目: Given a binary tree, determine if it is height-balanced. For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1. 题解: 采用递归的方法,要记录depth用来比较. 代码如下:…

题目: Given an array where elements are sorted in ascending order, convert it to a height balanced BST. 题解: 先复习下什么是二叉搜索树(引自Wikipedia): 二叉查找树(Binary Search Tree),也称有序二叉树(ordered binary tree),排序二叉树(sorted binary tree),是指一棵空树或者具有下列性质的二叉树: 若任意节点的左子树不空,则左子树…

题目: Given a binary tree, find its minimum depth. The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node. 题解: 递归解法急速判断左右两边子树哪个depth最小,要注意如果有个节点只有一边孩子时,不能返回0,要返回另外一半边的depth. 递归解法:              …

题目: Given a binary tree, find its maximum depth. The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. 题解: 递归解法:                                                            } 非递归解法,参考codegan…

题目: Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST. 题解: 之前做过一道是从sorted array转换到BinarySearchTree的,方法还是一样二分法.但是构造树的方法不是由顶至下了,是要由低至上的建立. 代码如下:          ListNode temp = head;                  …

题目: Given two binary trees, write a function to check if they are equal or not. Two binary trees are considered equal if they are structurally identical and the nodes have the same value. 题解: 递归判断左右是否相等. 代码如下:                                         …

题目: Follow up for N-Queens problem. Now, instead outputting board configurations, return the total number of distinct solutions. 题解: 这道题跟NQueens的解法完全一样(具体解法参照N QueensN Queens leetcode java),只不过要求的返回值不同了..所以要记录的result稍微改一下就好了... 因为涉及到递归,result传进去引用类型(…