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Language/Type: C++ linked lists pointers

Write a function named chopBothSides that accepts a reference to a pointer to the front of a linked list, and an integer parameter k, and removes k elements from the front of the list and k elements from the back of the list. Suppose a variable named front points to the front of a chain storing the following values:

{10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110}

The call of chopBothSides(front, 3); would change the list to store the following elements:

{40, 50, 60, 70, 80}

If we followed this by a second call of chopBothSides(front, 1);, the list would store the following elements:

{50, 60, 70}

If the list is not large enough to remove k elements from each side, do not modify the list and throw an integer exception. If the list contains exactly 2k elements, it should become empty as a result of the call. If k is 0 or negative, the list should remain unchanged. Do not leak memory; if you remove any nodes from the list, free their associated memory.


  • Your code should run in no worse than O(N) time, where N is the length of the list. (You may make more than one pass over the list, but the number of passes you make can't grow as k or N grow.)
  • Do not use any auxiliary data structures such as arrays, vectors, queues, strings, maps, sets, etc.
  • Do not modify the data field of any nodes; you must solve the problem by changing the links between nodes.
  • You may not construct new ListNode objects, though you may create as many ListNode* pointers as you like.

Assume that you are using the ListNode structure as defined below:

struct ListNode {
    int data;         // value stored in each node
    ListNode* next;   // pointer to next node in list (nullptr if none)
Function: Write a C++ function as described, not a complete program.

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