TCS NQT 2026 Coding Questions | Day 4: Find the Substring Index (First Occurrence) | Yellowmatics

Welcome to Day 4 of the Yellowmatics TCS NQT 2026 Series!
Today, we dive into string manipulation by solving the "Find the Substring Index" problem. This challenge asks you to return the index of the first occurrence of a needle string within a haystack string—without using built-in library functions like indexOf() or find().
In this video, we cover:
• Algorithm Logic: How to implement a manual sliding window search.
• Edge Cases: Handling empty strings, non-existent substrings, and cases where the needle is longer than the haystack.
• In-Place Search: Ensuring memory efficiency during the search process.
• Complexity Analysis: Why the brute-force approach is $O(n \times m)$ and how to optimize it.
This problem is essential for clearing the TCS NQT Foundation and Digital coding sections in the March 2026 cycle.
Problem Example:
• Input: Haystack = "yellowmatics", Needle = "mat"
• Output: 6

Видео TCS NQT 2026 Coding Questions | Day 4: Find the Substring Index (First Occurrence) | Yellowmatics канала Yellowmatics