Two Pointers Summary

背向双指针

• Longest Palindromic Substring的中心线枚举算法
• Find K Closest Elements

相向双指针

两根指针一头一尾，向中间靠拢直到相遇: while left < right

time complexity: O(n)

1. Reverse
   1. Recover rotated sorted array & rotate string（三步翻转法）
   2. Valid Palindrome
      1. follow up: 可以删掉一个字符的Valid Palindrome（证明题）
2. Two Sum
3. Partition

同向双指针

两根指针一前一后，直到前面的指针走过头

• Sliding Window
• Fast & Slow Pointers

time complexity: O(n)

1. Move Zeros Before solving the problem, you need to consider:
   • Does the number of zeros matter?
   • Should the result be in order or not?
   • How to minimize the times of writing zeros in the array?

Two Sum

Fast and Slow Pointers

Quick Sort

Merge Sort