练手题：
388. Longest Absolute File Path
390. Elimination Game *
392. Is Subsequence: 注意follow up *
393. UTF-8 Validation: 怎么感觉每一题都要拿来练一练？
394. Decode String
399. Evaluate Division
402. Remove K Digits: 再练一遍，争取bug free
413. Arithmetic Slices: 要利用些数学技巧
436. Find Right Interval
439. Ternary Expression Parser
450. Delete Node in a BST: 三种情况删除法非常痛苦，试试divide and conquer
464. Can I Win *
469. Convex Polygon: 说要总结，到现在都没动手，留下很多疑难问题，不能光记录不克服。。。*
474. Ones and Zeroes * 背包问题还是需要加强复习！！！
477. Total Hamming Distance
467. Unique Substrings in Wraparound String
473. Matchsticks to Square *
不会题：
418. Sentence Screen Fitting *
421. Maximum XOR of Two Numbers in an Array *
451. Sort Characters By Frequency: bucketsort 和heap两种做法
456. 132 Pattern *
