二分法简单但是边界值十分容易出错, 时间复杂度为O(log n)
mid = right + (left - right) / 2 防止left right 都大时候溢出
二分法剖析：Binary Search 二分搜索法 C++
bold - high frequency top 5
第一类 基本用法
Search Insert Position [easy, 2]
Find First and Last Position of Element in Sorted Array [medium, 2]
First Bad Version [easy, 2]
Find Peak Element [medium, 2]
Heaters [easy, 2] (解法二，第一个不小于)
Closest Binary Search Tree Value
Median of Two Sorted Arrays [hard, 1]
第二类 数学相关
Sqrt(X)
Pow(x, n)
FastPower
Arranging Coins [easy, 2] (数列，小心overflow)
Valid Perfect Square [easy, 3] (解法二，==)
第三类 2D binary search
Search a 2d Matrix
Search a 2d Matrix II
第四类 sorted or rotated array
Search in Rotated Sorted Array, II (duplicated allowed)
Find Min in Rotated Sorted Array, II (duplicated allowed)
利用Binary Search维护Longest Increasing Substring
维护一个vector，每一个元素代表 increasing substring position i 上最小的数
update: 小于首元素代替，大于末元素加在末尾，大于首元素小于末元素代替第一个比它大的元素
注：这个维护的vector并非最后的increasing substring，只是元素个数相同
Longest Increasing Subsequence [medium, 2]
Russian Doll Envelopes [hard, 2] (上面的升级版)
还想练手：
Increasing Triplet Subsequence [medium, 3]
未归类
Find Smallest Letter Greater Than Target
Find Kth Smallest Pair Distance
Find K Closest Elements
Find the Duplicate Number
Kth Smallest Number in Multiplication Table
Kth Smallest Element in a BST
Kth Smallest Element in a Sorted Matrix
Count Complete Tree Nodes
Divide Two Integers
Find Right Interval
4Sum II
Maximum Length of Repeated Subarray
Minimum Size Subarray Sum
Max Sum of Rectangle No Larger Than K [hard, 3]
Split Array Largest Sum
Kth Smallest Element in a Sorted Matrix
Count of Smaller Numbers After Self
Reference:
https://lefttree.gitbooks.io/leetcode-categories/BinarySearch/binarySearch.html
https://blog.csdn.net/linhuanmars/article/details/31354941
https://zxth93.github.io/2017/11/20/LeetCode-binary-search类总结/index.html