Solve linked list, string filtering, and puzzle

Coding & Algorithms (3 tasks)

1) Find the 5th node from the end (singly linked list)

You are given the head pointer of a singly linked list.

• Return the value of the node that is the 5th from the end (i.e., counting from the tail: tail is 1st).
• If the list has fewer than 5 nodes, specify a reasonable behavior (e.g., return null / throw an error).

Constraints: Aim for $O(n)$ time and $O(1)$ extra space.

2) Remove “camel-pattern” triplets from a string

Given a string s (ASCII letters only), remove every contiguous length-3 substring s[i..i+2] that matches the pattern:

• s[i] == s[i+2] (exact same character), and
• s[i] and s[i+1] have different letter cases (one uppercase, one lowercase).

After removals, the remaining parts are concatenated.

Example

• Input: "AaADbDEeEbcvQv"
• Output: "bc"

Clarify whether removals are single pass or repeated until no more matches; design your solution accordingly.

Constraints: $1 \le |s| \le 2\times 10^5$.

3) Gold bar daily pay puzzle

A worker works 7 days and is paid one gold bar total. The bar can be broken into pieces with at most two breaks.

• How can you pay the worker each day such that the daily payment is equal (i.e., each day receives exactly $\tfrac{1}{7}$ of the total bar value)?
• You may exchange pieces back and forth each day (give/take pieces) as long as the net pay per day is correct.