Gain insights into competitive programming, explore C++ skills with theory, code samples, practice problems, and master faster implementation for contests like ACM ICPC, Google CodeJam, and HackerCup.

Competitive programming can be a great way to build out your programming skills, get on any major company’s radar, and earn a little extra cash along the way.

In this course, you will learn to prepare for competitive programming contests like ACM ICPC, Google CodeJam, Facebook HackerCup, and many more.

Each topic is broken down with a healthy mix of theory, code samples, step-by-step solved sample problems, illustrations, useful practice problems, and tips and tricks for faster implementation.

You will need some solid C++ foundations coming into this course, but by the end it, you will be confident enough in your C++ skills to take home the win.

Competitive Programming in C++: The Keys to Success

# Problem statement
Given an array $A$ of $N$ integers. Answer $Q$ queries of the type $(l, r)$ - reverse the subarray $A[l...r]$. Print the array after each query.

**Input format**
The first line contains two integers $N$ and $Q$ $(1 \leq N, Q \leq 10^3)$. 

The second line contains $N$ space-separated integers representing the array $A[]$ $(1 \leq A[i] \leq 10^6)$. 

Next, $Q$ lines each contains pair of integers $l$ and $r$ $(1 \leq l \leq r \leq N)$.

---

# Sample
**Input**
```
5 3
1 2 3 4 5
1 5
2 3
3 5
```

**Output**
```
5 4 3 2 1
5 3 4 2 1
5 3 1 2 4
```

---

# Solution

For each query, we can reverse the given array in $O(N)$ time. Let's see how we would reverse the entire array; we can then do the same to reverse a subarray.


We start with two pointers, one at the start and one at the end of the array. Pointer 1 moves to the right and Pointer 2 moves to the left after each step. At each step, we swap the elements at the two pointers.

See the below illustrations for better understanding.

In this lesson, we'll discuss a solved problem about how to reverse the given subarray of an array.


Introduction

Complexity Analysis

Number Theory

Arrays and Vectors

Sieve of Eratosthenes

Strings

Sorting

Linked List

Stack

Queue

Binary Tree

2 Pointers

Heap

Binary Search Tree

Balanced Binary Search Tree

Course Conclusion

Solved Problem - Reverse Subarray

Problem statement