1. 二进制中1的个数:n=n&(n-1) 会把n中的最右边的1变为0;0011&0001=0001
2. 小顶堆升序,大顶堆降序
3. Given “pwwkew”, the answer is “wke”, with the length of 3. Note that the answer must be a substring, “pwke” is a subsequence and not a substring. 子序列可以不连续,子串必须连续
4. Search in rotate array 或 search insert position 都是二分查找