Remove Duplicate Letters | Lexicographically Smallest String | Greedy + Stack | Java Python C++

In this video, we solve the famous problem Remove Duplicate Letters to form the Lexicographically Smallest String using an Optimal Greedy + Stack approach.

The goal is to remove duplicate characters such that every letter appears only once and the final string is lexicographically smallest among all possible answers.

This problem is a classic combination of Greedy and Monotonic Stack where understanding when to keep or remove characters becomes the key intuition.

We first understand the brute force thinking of generating all possible subsequences, and then move to the optimized solution using stack, visited array/set, and last occurrence tracking.

In this video, you will learn:

Brute force intuition and why it is inefficient
How lexicographical order works
Greedy intuition behind removing characters
Why Monotonic Stack is used
Understanding last occurrence concept
When and why to pop elements from stack
Step-by-step dry run of the optimal solution
Time and space complexity analysis

This pattern is widely used in coding interviews and appears in multiple variations such as:

Remove K Digits
Smallest Subsequence of Distinct Characters
Monotonic Stack Problems
Greedy String Problems

Mastering this pattern will help you solve many advanced Stack + Greedy interview questions efficiently.

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Видео Remove Duplicate Letters | Lexicographically Smallest String | Greedy + Stack | Java Python C++ канала RisingBrain