Count Equal-Value Index Pairs
Company: Google
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Other
### Problem
Count pairs of indices(i,j) with i<j and nums[i]==nums[j]. Each pair of positions counts separately.
```cpp
class Solution {
public:
int numIdenticalPairs(vector<int>& nums);
};
```
### Examples
**Example 1:**
```text
Input: nums = [2,3,2,3,2]
Output: 4
Explanation: Three2s form three pairs,and two3s form one more.
```
**Example 2:**
```text
Input: nums = [5]
Output: 0
Explanation: There are not two different indices.
```
### Constraints
- nums has length 1 to 100.
- Every value lies in `[1,100]`.
### Contract considerations
Equality of values is required; distinct positions may hold the same value.
```hint Read the boundary condition
Count index pairs rather than distinct value pairs. Exclude self-pairs and reversed copies of the same pair.
```
### Boundary reminders
Equality of values is required; distinct positions may hold the same value.
Overview: Count Equal-Value Index Pairs. Count pairs of indices(i,j) with i<j and nums[i]==nums[j]. Each pair of positions counts separately.