4) Remove Zero Sum Consecutive Nodes from Linked List

Hi geeks! In this article, we going to play with Linked list and hash map by solving this interesting problem remove Zero Sum Consecutive Nodes from Linked List.

Given the head of a linked list, we repeatedly delete consecutive sequences of nodes that sum to 0 until there are no such sequences.

After doing so, return the head of the final linked list.  You may return any such answer.

(Note that in the examples below, all sequences are serializations of ListNode objects.)

Example 1:

Input: head = [1,2,-3,3,1]
Output: [3,1]
Note: The answer [1,2,1] would also be accepted.

Example 2:

Input: head = [1,2,3,-3,4]
Output: [1,2,4]

Example 3:

Input: head = [1,2,3,-3,-2]
Output: [1]

Solution:

public ListNode removeZeroSumSublists(ListNode head) {
        ListNode dummy = new ListNode(0), cur = dummy;
        dummy.next = head;
        int prefix = 0;
        Map<Integer, ListNode> m = new HashMap<>();
        while (cur != null) {
            prefix += cur.val;
            if (m.containsKey(prefix)) {
                cur =  m.get(prefix).next;
                int p = prefix + cur.val;
                while (p != prefix) {
                    m.remove(p);
                    cur = cur.next;
                    p += cur.val;
                }
                m.get(prefix).next = cur.next;
            } else {
                m.put(prefix, cur);
            }
            cur = cur.next;
        }
        return dummy.next;
    }

Detailed Explanations:

Time Complexity : O(n)

Space Complexity : O(n) Since we used the HashMap for storing the List.

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