Description:
The thief has found himself a new place for his thievery again. There is only one entrance to this area, called the “root.” Besides the root, each house has one and only one parent house. After a tour, the smart thief realized that “all houses in this place forms a binary tree”. It will automatically contact the police if two directly-linked houses were broken into on the same night.
Description:
Given two words (start and end), and a dictionary, find the length of shortest transformation sequence from start to end, such that:
- Only one letter can be changed at a time
- Each intermediate word must exist in the dictionary
Description:
Clone an undirected graph. Each node in the graph contains alabeland a list of itsneighbors.How we serialize an undirected graph:
Nodes are labeled uniquely.
We use
#as a separator for each node, and,as a separator for node label and each neighbor of the node.As an example, consider the serialized graph
{0,1,2#1,2#2,2}.
Description:
Given an directed graph, a topological order of the graph nodes is defined as follow:
- For each directed edge A -> B in graph, A must before B in the order list.
- The first node in the order can be any node in the graph with no nodes direct to it.
Find any topological order for the given graph.
Description:
Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, …) which sum to n.
Example:
Given n = 12, return 3 because 12 = 4 + 4 + 4
Given n = 13, return 2 because 13 = 4 + 9
Description:
Given n nodes labeled from 0 to n - 1 and a list of undirected edges (each edge is a pair of nodes), write a function to check whether these edges make up a valid tree.
Notice:
- You can assume that no duplicate edges will appear in edges. Since all edges are undirected, [0, 1] is the same as [1, 0] and thus will not appear together in edges.
Example:
Given n = 5 and edges = [[0, 1], [0, 2], [0, 3], [1, 4]], return true.
Given n = 5 and edges = [[0, 1], [1, 2], [2, 3], [1, 3], [1, 4]], return false.
分析：
如果要组成一棵树，要满足下面两个条件：
Convert Sorted List to Balanced BST
Description:
Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.
Example:
2
1->2->3 => /
1 3
分析：
Description:
Given a sequence {an}, how many non-empty sub-sequence of it is a prefix of fibonacci sequence.
A sub-sequence is a sequence that can be derived from another sequence by deleting some elements without changing the order of the remaining elements.
The fibonacci sequence is defined as below:
Description:
Little Hi and Little Ho are playing a construction simulation game. They build N cities (numbered from 1 to N) in the game and connect them by N-1 highways. It is guaranteed that each pair of cities are connected by the highways directly or indirectly.
The game has a very important value called Total Highway Distance (THD) which is the total
Binary Tree Zigzag Level Order Traversal
Description:
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).
Example
Given binary tree {3,9,20,#,#,15,7},