📅 Date: Feb 12, 2026
🔥 Topic: Difference between Subarray & Subsequence

🧐 Are they the same?

No! This is the most common confusion in interviews.

Feature Subarray Subsequence
Definition Contiguous part of array. Derived by deleting elements, Order matters.
Continuity Must be continuous. Can be non-continuous.
Total Count N * (N+1) / 2 2^N (Power Set)

🧠 Visual Example

Let Array = [1, 2, 3, 4]

✅ Valid Subarrays

  • [1, 2] (Connected)
  • [2, 3, 4] (Connected)
  • [3] (Single element is also contiguous)

❌ Invalid Subarray

  • [1, 3] (Skipped 2, so NOT a subarray)

✅ Valid Subsequences

  • [1, 2]
  • [1, 3] (Valid! We just deleted 2)
  • [1, 2, 4] (Valid! We deleted 3)

💻 Day 42 Code: Printing All Subarrays

Printing subsequences requires Recursion (coming soon). Printing subarrays just needs 3 loops. 

#include <iostream>
using namespace std;

int main() {
    int arr[] = {1, 2, 3, 4};
    int n = 4;

    cout << "All Subarrays:" << endl;

    for(int start=0; start<n; start++) {
        for(int end=start; end<n; end++) {
            
            // Print elements between start and end
            cout << "[ ";
            for(int k=start; k<=end; k++) {
                cout << arr[k] << " ";
            }
            cout << "]" << endl;
        }
    }
    return 0;
}

💭 Thoughts

Subarray = Slices of bread (Connected).
Subsequence = Picking toppings (Can skip, but order stays same).
Clear concept helps in solving Hard DP problems later.