---
id: 2P
title: "Two Pointers"
author: Darren Yao
prerequisites:
 - 
     - Silver - Sorting
---

<module-excerpt>

**Two pointers** refers to iterating two monotonic pointers across an array to search for a pair of indices satisfying some condition in $O(n)$ time.

</module-excerpt>

## Tutorials

 - Intro to USACO 14.1
 - CPH 8.1

## Problems

 - CSES
   - [Sum of Two Values](https://cses.fi/problemset/task/1640)
 - USACO
   - [Silver - Diamond Collector](http://usaco.org/index.php?page=viewproblem2&cpid=643)
     - sort and then use 2P
   - [Silver - Paired Up](http://usaco.org/index.php?page=viewproblem2&cpid=738)
     - sort and then use 2P
   - [Gold - Haybale Feast](http://usaco.org/index.php?page=viewproblem2&cpid=767)
     - just 2P with additional set
 - CF
   - [Books](https://codeforces.com/problemset/problem/279/B)
   - [Cellular Network](http://codeforces.com/problemset/problem/702/C) [](48)
   - [USB vs. PS/2](http://codeforces.com/problemset/problem/762/B) [](53)
   - [K-Good Segment](http://codeforces.com/problemset/problem/616/D) [](53)
   - [(Long Title)](http://codeforces.com/problemset/problem/814/C) [](54)
   - [Jury Meeting](http://codeforces.com/problemset/problem/853/B) [](90)

## Extensions

The two pointers technique can be extended to the two dimensional sliding window algorithm. If you're looking for a more challenging problem using 2-D sliding window, see [USACO Plat Fort Moo](http://usaco.org/index.php?page=viewproblem2&cpid=600).