Keep One Representative of Each Sorted List Value
Company: Google
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Other
### Problem
Given the head of a sorted singly linked list, remove excess copies so each distinct value appears once. Return the head of the resulting sorted linked list. A value that appeared repeatedly must still have one representative.
The supplied `ListNode` has `val` and `next` fields:
```cpp
ListNode* deleteDuplicates(ListNode* head);
```
Brackets in examples display values along the pointer chain.
### Examples
```text
Input: head = [-3,-3,0,0,0,5]
Output list: [-3,0,5]
```
```text
Input: head = [7,7,7]
Output list: [7]
```
### Constraints
- There are between 0 and 300 nodes.
- Every node value is between -100 and 100, inclusive.
- The input list is sorted in ascending order, allowing equal values.
Overview: Collapse each equal-value run of a sorted linked list to one representative while retaining the pointer interface.