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. Rising Brain (DSA Sheet): Rising Brain (DSA Sheet) Connect with me here: LinkedIn – Anjali Kumari LinkedIn Instagram – rbanjali.codes Instagram Twitter (X) – Anjali Kumari on X