K-th Sum (Codeforces EDU) | Binary Search on Pair Sums + New Pattern: K-th Element Problems

n this video, we dive into the 𝐊-𝐭𝐡 𝐒𝐮𝐦 problem from the 𝐂𝐨𝐝𝐞𝐟𝐨𝐫𝐜𝐞𝐬 𝐄𝐃𝐔 𝐁𝐢𝐧𝐚𝐫𝐲 𝐒𝐞𝐚𝐫𝐜𝐡 Track, and learn a powerful new concept — how to solve K-th Element problems using Binary Search on the Answer.⁣ ⁣ 🔍 You're given two arrays a[] and b[], and the task is to find the K-th smallest sum of pairs formed by choosing one element from each array.⁣ ⁣ ⚠️ A naive O(n²) solution will lead to TLE. Instead, we binary search over all possible sums and, for each candidate, count how many valid pairs exist using upper_bound — a classic optimization for sorted arrays.⁣ ⁣ 🎯 In This Video, You’ll Learn:⁣ - A new problem-solving pattern: K-th Element via Binary Search⁣ - How to apply binary search on answers smartly⁣ - How to count pairs efficiently using upper_bound⁣ - Time & space optimizations for interview-level performance⁣ ⁣ 📈 Difficulty: Medium-Hard⁣ 🧠 Core Concepts:⁣ - Binary Search on Answer Space⁣ - Counting Valid Pairs in Sorted Arrays⁣ - Efficient Sum Bounds Checking ⁣ - K-th Element Type Problems (very common in interviews)⁣ ⁣ 🔗 Problem Source: Codeforces EDU — Binary Search Track⁣ 🔗Problem Link: https://codeforces.com/edu/course/2/lesson/6/5/practice/contest/285084/problem/C⁣ 📂 Series: Advanced Binary Search Patterns