What is the Two Pointers Technique:

uses two index variables to traverse a linear data structure—like an array, string, or linked list—to solve problems efficiently without nested loops.

Why Use it ?

Time Efficiency: It often reduces time complexity from O(n²) (using nested loops) down to linear time O(n).

Space Efficiency: It typically requires constant space O(1) because it only tracks a few indices.

Whats Patterns of 2 Pointers

Pattern 1 (Variable_Size)

1.1 Opposite Direction (Converging Pointers): One pointer starts at the beginning (left = 0) and the other at the end (right = n — 1). They move toward each other until they meet. ​Best Used For: Sorted arrays, pair sum problems (ex: Two Sum on sorted input), or checking palindromes.

Problem: Can you choose two indices i , j (i≠j) and ai+aj=K If you can choose to indices solving the equation print "YES" otherwise "NO"

Brute Force Approach (TLE-->O(N^2))

int n; long long x; cin >> n >> x;

vector<long long> arr(n);
for (int i = 0; i < n; i++) {
    cin >> arr[i];
}

// Brute Force: Check every pair (i, j) where i != j
for (int i = 0; i < n; i++) {
    for (int j = i + 1; j < n; j++) {
        if (arr[i] + arr[j] == x) {
            cout << "YES\n";
            return 0;
        }
    }
}


cout << "NO\n";