- array 连续值
- array 双指针
- array 排序去除
- array 从两边夹向中间 product of array except self
- array 从中间向两边散开 Longest - Palindromic Substring
- array也可以倒着考虑，从后往前 –》 merge sorted aray
Sliding windows: 固定一个增加(++),另一个不定增加
Spreading from the center
Try all possible i and find the longest palindromic string whose center is i (odd case) and i / i + 1 (even case).
