Leetcode #2148: Count Elements With Strictly Smaller and Greater Elements
In this guide, we solve Leetcode #2148 **Count Elements With Strictly Smaller and Greater Elements ** in Python and focus on the core idea that makes the solution efficient.
You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.
Problem Statement
Given an integer array nums, return the number of elements that have both a strictly smaller and a strictly greater element appear in nums. Example 1: Input: nums = [11,7,2,15] Output: 2 Explanation: The element 7 has the element 2 strictly smaller than it and the element 11 strictly greater than it.
Quick Facts
- Difficulty: Easy
- Premium: No
- Tags: Array, Counting, Sorting
Intuition
Sorting reveals structure that is hard to see in the original order.
Once sorted, a linear scan is usually enough to compute the answer.
Approach
Sort the data and sweep through it while maintaining a small state.
This keeps the logic straightforward and reliable.
Steps:
- Sort the data.
- Scan in order while maintaining state.
- Update the best answer.
Example
Input: nums = [11,7,2,15]
Output: 2
Explanation: The element 7 has the element 2 strictly smaller than it and the element 11 strictly greater than it.
Element 11 has element 7 strictly smaller than it and element 15 strictly greater than it.
In total there are 2 elements having both a strictly smaller and a strictly greater element appear in nums.
Python Solution
class Solution:
def countElements(self, nums: List[int]) -> int:
mi, mx = min(nums), max(nums)
return sum(mi < x < mx for x in nums)
Complexity
The time complexity is , where is the length of the array . The space complexity is .
Edge Cases and Pitfalls
Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.
Summary
This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.