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2358 - Maximum Number of Groups Entering a Competition (Medium)

https://leetcode.com/problems/maximum-number-of-groups-entering-a-competition

Problem Statement​

You are given a positive integer array grades which represents the grades of students in a university. You would like to enter all these students into a competition in ordered non-empty groups, such that the ordering meets the following conditions:

  • The sum of the grades of students in the ith group is less than the sum of the grades of students in the (i + 1)th group, for all groups (except the last).
  • The total number of students in the ith group is less than the total number of students in the (i + 1)th group, for all groups (except the last).

Return the maximum number of groups that can be formed.

Example 1:

Input: grades = [10,6,12,7,3,5]
Output: 3
Explanation: The following is a possible way to form 3 groups of students:
- 1st group has the students with grades = [12]. Sum of grades: 12. Student count: 1
- 2nd group has the students with grades = [6,7]. Sum of grades: 6 + 7 = 13. Student count: 2
- 3rd group has the students with grades = [10,3,5]. Sum of grades: 10 + 3 + 5 = 18. Student count: 3
It can be shown that it is not possible to form more than 3 groups.

Example 2:

Input: grades = [8,8]
Output: 1
Explanation: We can only form 1 group, since forming 2 groups would lead to an equal number of students in both groups.

Constraints:

  • 1 <= grades.length <= 10^5
  • 1 <= grades[i] <= 10^5

Approach: Math​

We need to form groups of 1, 2, 3, ... students in order to maximize the number of groups. We can use the formula i * (i + 1) / 2 to find out the number of students in i groups.

Written by @wingkwong
class Solution {
public:
    int maximumGroups(vector<int>& grades) {
        int n = grades.size(), i = 0;
        while (i * (i + 1) / 2 <= n) i++;
        return i - 1;
    }
};