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Java-based LeetCode algorithm problem solutions, regularly updated
2860\. Happy Students
Medium
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.
The ith
student will become happy if one of these two conditions is met:
* The student is selected and the total number of selected students is **strictly greater than** `nums[i]`.
* The student is not selected and the total number of selected students is **strictly** **less than** `nums[i]`.
Return _the number of ways to select a group of students so that everyone remains happy._
**Example 1:**
**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.
**Example 2:**
**Input:** nums = [6,0,3,3,6,7,2,7]
**Output:** 3
**Explanation:**
The three possible ways are:
The class teacher selects the student with index = 1 to form the group.
The class teacher selects the students with index = 1, 2, 3, 6 to form the group.
The class teacher selects all the students to form the group.
**Constraints:**
* 1 <= nums.length <= 105
* `0 <= nums[i] < nums.length`