最近在看coursera上面普林斯顿大学的算法课，关于归并排序有三点改进方法。

leetcode algorithms #5. Title: Longest Palindromic Substring

leetcode algorithms #4. Title: 两个排序数组的中位数.这题还没搞

leetcode algorithms #3. Title: Longest Substring Without Repeating Characters

leetcode algorithms #2. Title: Add Two Numbers

leetcode algorithms #1. Title: Two sum