LeetCode 496 | Next Greater Element I | Python Monotonic Stack | AlgoYogi

Welcome to AlgoYogi! 🚀 Start Your Smart Coding Prep at 👉 https://algoyogi.io In this video, we solve **LeetCode 496: Next Greater Element I** using Python and an efficient **monotonic stack** approach. Problem Brief: You are given two arrays—nums1 (a subset of nums2) and nums2. For each element in nums1, find the first greater element to its right in nums2. If none exists, return -1. Approach: 1) Traverse nums2 from left to right, using a stack to maintain a decreasing sequence of numbers. 2) While the current number is greater than the stack top, pop from the stack and record that the popped number’s next greater element is the current one. 3) Push the current number onto the stack. 4) After processing nums2, any remaining stack elements have no greater element—default to -1. 5) Build results for nums1 using the precomputed mapping. Example: nums1 = [4, 1, 2], nums2 = [1, 3, 4, 2] - 4 → -1, 1 → 3, 2 → -1 Answer: [-1, 3, -1] --- ### ⏱ Timestamps 0:00 Introduction 0:20 Problem Statement 1:00 Approach 13:30 Python Code Walkthrough 17:00 Time & Space Complexity --- ### Why Watch? - Learn the power of the **monotonic stack pattern** for next-greater queries - Avoid inefficient nested loops; use O(n + m) time with O(n) space - Great technique for many related LeetCode problems ([turn0search0], [turn0search2], [turn0search3]) #LeetCode #NextGreaterElementI #Python #MonotonicStack #AlgoYogi