👨‍💻 By Expert Funda 📅 Thursday, March 19, 2026

DSA Sheet - Day 3 Arrays

DSA Sheet Day 3 - Arrays | ExpertFunda

🚀 DSA Sheet – Day 3: Arrays (Part 3)

This set introduces advanced patterns like Sliding Window, Backtracking, and Interval Merging. These are highly frequent in FAANG interviews — focus on understanding patterns deeply.

📊 Progress Tracker

Progress: 0 / 6 Completed

Done Problem Practice Level Companies
Next Permutation Solve Medium Adobe, Goldman Sachs, Uber
Merge Overlapping Intervals Solve Medium Google
Longest Substring Without Repeating Solve Medium Amazon, Morgan Stanley
Set Matrix Zeroes Solve Medium Amazon, Microsoft
Word Search Solve Medium Google, Goldman Sachs, Ola
Product of Array Except Self Solve Medium Amazon

🧠 Key Approaches

  • Next Permutation: Find breakpoint → swap → reverse suffix
  • Merge Intervals: Sort intervals, merge overlaps
  • Longest Substring: Sliding window + HashSet
  • Set Matrix Zeroes: Use first row/column as markers
  • Word Search: Backtracking (DFS)
  • Product Except Self: Prefix + suffix multiplication

⚡ Quick Cheatsheet

Merge Intervals


sort(intervals.begin(), intervals.end());
vector> res;

for(auto it : intervals){
  if(res.empty() || res.back()[1] < it[0]) 
    res.push_back(it);
  else 
    res.back()[1] = max(res.back()[1], it[1]);
}

Longest Substring Without Repeating Characters


set s;
int l = 0, res = 0;

for(int r = 0; r < n; r++){
  while(s.count(str[r])) 
    s.erase(str[l++]);

  s.insert(str[r]);
  res = max(res, r - l + 1);
}

Product of Array Except Self


vector res(n, 1);

for(int i = 1; i < n; i++) 
  res[i] = res[i - 1] * nums[i - 1];

int suffix = 1;

for(int i = n - 1; i >= 0; i--){
  res[i] *= suffix;
  suffix *= nums[i];
}

🔥 Pro Tip

These problems unlock advanced patterns:
  • Sliding Window
  • Backtracking (DFS)
  • Interval Merging
Master these and medium-level problems will start feeling easy.
Continue Reading →