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 a **sorted** array of $N$ integers $A[]$. Find if there exists a triplet of integers $A[i]$, $A[j]$ and $A[k]$ such that the sum is equal to given integer $X$.

**Input format**

The first line of input consists of two space-separated integers $N(1 \leq N \leq 10^{5})$ and $X(1 \leq X \leq 10^{6})$.

The next line contains $N$ space-separated integers representing the array $A[](1 \leq A[i] \leq 10^{5})$.

**Output format**

Print a single line of three space-separated integers $i$, $j$ and $k$ such that $A[i] + A[j] + A[k] = X$ or print $-1$ if there is no such triplet.

---

# Sample

**Input**

```
6 35
2 4 7 10 15 16
```

**Output**

```
2 5 6
```

---

# Explanation

$2^{nd}$, $5^{th}$ and $6^{th}$ element of $A[]$ add upto $35$.

$A[2] = 4$

$A[5] = 15$

$A[6] = 16$

---

# Brute force

Use three loops to iterate over the array and check all ${N} \choose {3}$ pairs. Time complexity is $O(N^{3})$.

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# Optimize to $O(N^{2})$

The algorithm is a slight modification of the Pair sum problem discussed earlier. If we iterate over the array for $i$ then we need to find a pair in the array $A[i+1...N]$ that adds to $X-A[i]$.

The second part is exactly the previous problem. 

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 - Triplet Sum

Problem statement