Hello everyone!↵
↵
Today I want to explain one of the most useful techniques in competitive programming — Two Pointers↵
* What is Two Pointers?↵
↵
Two pointers is a technique where we use two indices to iterate over an array or string.↵
↵
Usually:↵
↵
* One pointer starts from the beginning↵
* Another from the end (or also from beginning)↵
↵
* Example Problem↵
↵
Given an array, find if there exist two numbers whose sum equals k.↵
↵
* Idea↵
↵
1. Sort the array↵
↵
2. Set:↵
↵
left = 0↵
right = n — 1↵
↵
3. While left < right:↵
↵
if a[left] + a[right] == k → FOUND↵
if sum < k → left++↵
if sum > k → right--↵
↵
* Code (C++)↵
↵
```cpp↵
#include <bits/stdc++.h>↵
using namespace std;↵
↵
int main() {↵
int n, k;↵
cin >> n >> k;↵
vector<int> a(n);↵
for(int i = 0; i < n; i++) cin >> a[i];↵
sort(a.begin(), a.end());↵
int l = 0, r = n — 1;↵
while(l < r) {↵
int sum = a[l] + a[r];↵
if(sum == k) {↵
cout << "YES\n";↵
return 0;↵
}↵
else if(sum < k) l++;↵
else r--;↵
}↵
cout << "NO\n";↵
}↵
```↵
* Complexity↵
↵
Sorting: O(n log n)↵
Two pointers: O(n)↵
↵
Total: O(n log n)↵
↵
* When to Use?↵
↵
1) Sorted arrays↵
2)Pair problems↵
3)Subarray problems↵
↵
*Final Tip↵
↵
If you see:↵
↵
1) “find pair”↵
2) “sum equals k”↵
3) “continuous segment”↵
Think about Two Pointers↵
↵
Thanks for reading! If this helped you, please upvote
↵
Today I want to explain one of the most useful techniques in competitive programming — Two Pointers↵
* What is Two Pointers?↵
↵
Two pointers is a technique where we use two indices to iterate over an array or string.↵
↵
Usually:↵
↵
* One pointer starts from the beginning↵
* Another from the end (or also from beginning)↵
↵
* Example Problem↵
↵
Given an array, find if there exist two numbers whose sum equals k.↵
↵
* Idea↵
↵
1. Sort the array↵
↵
2. Set:↵
↵
left = 0↵
right = n — 1↵
↵
3. While left < right:↵
↵
if a[left] + a[right] == k → FOUND↵
if sum < k → left++↵
if sum > k → right--↵
↵
* Code (C++)↵
↵
```cpp↵
#include <bits/stdc++.h>↵
using namespace std;↵
↵
int main() {↵
int n, k;↵
cin >> n >> k;↵
vector<int> a(n);↵
for(int i = 0; i < n; i++) cin >> a[i];↵
sort(a.begin(), a.end());↵
int l = 0, r = n — 1;↵
while(l < r) {↵
int sum = a[l] + a[r];↵
if(sum == k) {↵
cout << "YES\n";↵
return 0;↵
}↵
else if(sum < k) l++;↵
else r--;↵
}↵
cout << "NO\n";↵
}↵
```↵
* Complexity↵
↵
Sorting: O(n log n)↵
Two pointers: O(n)↵
↵
Total: O(n log n)↵
↵
* When to Use?↵
↵
1) Sorted arrays↵
2)Pair problems↵
3)Subarray problems↵
↵
*Final Tip↵
↵
If you see:↵
↵
1) “find pair”↵
2) “sum equals k”↵
3) “continuous segment”↵
Think about Two Pointers↵
↵
Thanks for reading! If this helped you, please upvote
