LeetCode: Remove Zero Sum Consecutive Nodes from Linked List

Posted on August 25, 2019July 26, 2020 by braindenny

Remove Zero Sum Consecutive Nodes from Linked List

Similar Problems:

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]

Constraints:

The given linked list will contain between 1 and 1000 nodes.
Each node in the linked list has -1000 <= node.val <= 1000.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

Solution:

// https://code.dennyzhang.com/remove-zero-sum-consecutive-nodes-from-linked-list
// Basic Ideas: dummyNode + presum + hashmap
//
// Complexity: Time O(n), Space O(n)
/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func removeZeroSumSublists(head *ListNode) *ListNode {
    m := map[int]*ListNode{}
    dummyNode := ListNode{0, head}
    presum := 0
    p := &dummyNode
    for p != nil {
        presum += p.Val
        node , ok := m[presum]
        if ok {
            // remove previous presum
            v := presum
            q := node.Next
            for q!=p {
                v += q.Val
                delete(m, v)
                q = q.Next
            }
            // remove nodes
            node.Next = p.Next
            p = node
        } else {
            m[presum] = p
        }
        p = p.Next
    }
    return dummyNode.Next
}

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