Watermelon Problem (Codeforces 4A) Explained

One of the classic beginner problems on Codeforces is the Watermelon Problem (Problem 4A). It’s a simple yet interesting problem that helps new programmers understand conditional logic in C++.

Problem Statement

You are given a watermelon of weight n (where 1 ≤ n ≤ 100). Two friends want to divide it into two even positive parts. Your task is to determine whether it’s possible to split the watermelon as per their wish.

If the watermelon can be split into two even positive parts, print YES, otherwise print NO.

Approach

To solve this problem, we need to check two conditions:

1. The weight must be greater than 2 (since the smallest even split possible is 2 + 2 = 4).
2. The weight must be even (because two even parts can only sum up to an even number).

If both conditions are satisfied, then the answer is YES, otherwise it is NO.

Code Implementation

// https://codeforces.com/problemset/problem/4/A
#include <iostream>
using namespace std;

int main()
{
    int n = 0;
    cin >> n;
    if (((n - 2) % 2 == 0) && (n - 2 > 0))
    {
        cout << "YES";
    }
    else
    {
        cout << "NO";
    }
    puts("");
    return 0;
}

Code Explanation

1. Input Handling: We declare an integer variable n and read the input using cin. This represents the watermelon’s weight.

2. Logic Check:

   • (n - 2) % 2 == 0 ensures that after removing 2 from the weight, the remainder is still even.
   • (n - 2 > 0) ensures that the split results in two positive even numbers.

   Together, these checks confirm if the watermelon can be split into two even parts.

3. Output:

   • If the conditions are satisfied, we print YES.
   • Otherwise, we print NO.

4. End of Program: The puts("") prints a newline character, and return 0; indicates successful program execution.

Example Runs

• Input: 8 Output: YES (The watermelon can be split into 4 + 4.)

• Input: 5 Output: NO (Since 5 is odd, it can’t be split into two even parts.)

• Input: 2 Output: NO (Although 2 is even, it can’t be split into two positive even parts.)

Conclusion

The Watermelon problem is a great warm-up exercise for beginners learning C++. It introduces conditional statements, modulo operation, and input/output handling. Despite its simplicity, it reinforces the importance of breaking down conditions carefully when solving programming problems.