ToDo

Reading:
BIT: https://www.topcoder.com/community/data-science/data-science-tutorials/binary-indexed-trees/
Binary Search: https://www.topcoder.com/community/competitive-programming/tutorials/binary-search/
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Word Break II, java遍历写一遍
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Subset 所有解法再过一次 http://shibaili.blogspot.com/2013/06/day-38-77-combinations.html

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721 Accounts Merge 用DFS写一遍： http://shibaili.blogspot.com/2018/06/721-accounts-merge.html

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394. Decode String stack 再写一次

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Done
218. The Skyline Problem 再写一次

http://shibaili.blogspot.com/2015/06/day-110-skyline-problem.html
ref： https://briangordon.github.io/2014/08/the-skyline-problem.html

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再实现一次heap

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写一遍：https://leetcode.com/problems/longest-palindromic-subsequence/description/

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wildcard matching，regular expression再写一次

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Done
Word Ladder II 再写一次
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Valid number
regex，state machine跟普通方法都写一次

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772. Basic Calculator III
http://shibaili.blogspot.com/2018/08/772-basic-calculator-iii.html 用通解把I，II再写一次
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269. Alien Dictionary
代码精简一下。
bfs写一次
http://shibaili.blogspot.com/2018/08/269-alien-dictionary.html

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403. Frog Jump
2d-array写一次

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再写一次同一类型的题
reverse pair
Count of Smaller Numbers After Self
Count of Range Sum
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改进UnionFind
399. Evaluate Division

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心情好的时候把这个写一下：
308. Range Sum Query 2D - Mutable
https://leetcode.com/problems/range-sum-query-2d-mutable/description/

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再写一次
449. Serialize and Deserialize BST

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Greedy, 贪心算法能保证最优解吗？
https://leetcode.com/problems/course-schedule-iii/description/

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BFS
http://shibaili.blogspot.com/2018/10/329-longest-increasing-path-in-matrix.html

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二分法的一种写法是不设base case，然后由while里的条件来结束，最后返回left
https://shibaili.blogspot.com/2015/01/day-94-find-peak-element.html

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465. Optimal Account Balancing

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818. Race Car
DP的iterative写法

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753. Cracking the Safe
为什么for loop里面顺序要倒着