Explain event delegation in JavaScript. How does it improve performance when managing events on multiple elements? Provide an example of a scenario where you would use it.

**LeetCode #15 - 3Sum**\nGiven an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0. You may return the answer in any order.\n\n### Example 1:\n**Input:** nums = [-1,0,1,2,-1,-4]\n**Output:** [[-1,-1,2],[-1,0,1]]\n**Explanation:** The only triplet is [-1,-1,2] and [-1,0,1].\n\n### Example 2:\n**Input:** nums = [0,1,1]\n**Output:** []\n**Explanation:** No triplet adds up to zero.\n\n### Constraints:\n* 0 <= nums.length <= 3000\n* -10^5 <= nums[i] <= 10^5\n

**System Design: Design a URL Shortener**\nYou are tasked with designing a URL shortening service like bit.ly. Users input a long URL, and the service provides a shorter, unique URL. The system should handle a large number of requests and scale efficiently. Focus on how to generate the unique URLs, store them, and retrieve the corresponding long URLs. Consider the trade-offs between storage efficiency and speed of access in your design.