Leetcode #2860: Happy Students
In this guide, we solve Leetcode #2860 Happy Students 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
You are given a 0-indexed integer array nums of length n where n is the total number of students in the class. The class teacher tries to select a group of students so that all the students remain happy.
Quick Facts
- Difficulty: Medium
- Premium: No
- Tags: Array, Enumeration, 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 = [1,1]
Output: 2
Explanation:
The two possible ways are:
The class teacher selects no student.
The class teacher selects both students to form the group.
If the class teacher selects just one student to form a group then the both students will not be happy. Therefore, there are only two possible ways.
Python Solution
class Solution:
def countWays(self, nums: List[int]) -> int:
nums.sort()
n = len(nums)
ans = 0
for i in range(n + 1):
if i and nums[i - 1] >= i:
continue
if i < n and nums[i] <= i:
continue
ans += 1
return ans
Complexity
The time complexity is , and the space complexity is . 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.