### 3Sum The 3Sum problem requires finding triplets in an array that sum to a target (typically zero). Common approaches include sorting and using two-pointer techniques for \(O(n^2)\) efficiency. ### Recurrence Equation Recurrence equations define problems in terms of smaller subproblems, often used in dynamic programming or divide-and-conquer, such as \( T(n) = T(n/2) + O(n) \).