哈希表、映射、集合实战题目 / 课后作业
https://leetcode-cn.com/problems/valid-anagram/description/
https://leetcode-cn.com/problems/group-anagrams/
https://leetcode-cn.com/problems/two-sum/description/
树实战题目 / 课后作业 参考：
https://leetcode-cn.com/problems/binary-tree-inorder-traversal/
https://leetcode-cn.com/problems/binary-tree-preorder-traversal/
https://leetcode-cn.com/problems/n-ary-tree-postorder-traversal/
https://leetcode-cn.com/problems/n-ary-tree-preorder-traversal/
https://leetcode-cn.com/problems/n-ary-tree-level-order-traversal/
堆、二叉堆实战例题
https://leetcode-cn.com/problems/zui-xiao-de-kge-shu-lcof/
https://leetcode-cn.com/problems/sliding-window-maximum/
https://leetcode-cn.com/problems/top-k-frequent-elements/
课后作业
HeapSort ：自学 https://www.geeksforgeeks.org/heap-sort/
https://leetcode-cn.com/problems/chou-shu-lcof/
https://leetcode-cn.com/problems/top-k-frequent-elements/
图参考：
连通图个数： https://leetcode-cn.com/problems/number-of-islands/
拓扑排序（Topological Sorting）： https://zhuanlan.zhihu.com/p/34871092
最短路径（Shortest Path）：Dijkstra https://www.bilibili.com/video/av25829980?from=search&seid=13391343514095937158
最小生成树（Minimum Spanning Tree）： https://www.bilibili.com/video/av84820276?from=search&seid=17476598104352152051
本周作业 简单： 写一个关于 HashMap 的小总结。 说明：对于不熟悉 Java 语言的同学，此项作业可选做。
https://leetcode-cn.com/problems/valid-anagram/description/
https://leetcode-cn.com/problems/two-sum/description/
https://leetcode-cn.com/problems/n-ary-tree-preorder-traversal/description/
HeapSort ：自学 https://www.geeksforgeeks.org/heap-sort/
中等：
https://leetcode-cn.com/problems/group-anagrams/
https://leetcode-cn.com/problems/binary-tree-inorder-traversal/
https://leetcode-cn.com/problems/binary-tree-preorder-traversal/
https://leetcode-cn.com/problems/n-ary-tree-level-order-traversal/
https://leetcode-cn.com/problems/chou-shu-lcof/
https://leetcode-cn.com/problems/top-k-frequent-elements/
下周预习
预习题目：
爬楼梯
括号生成
Pow(x, n)
子集
N 皇后