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Formatted question description: https://leetcode.ca/all/1171.html

# 1171. Remove Zero Sum Consecutive Nodes from Linked List

Medium

## Description

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:

Output: [3,1]

Note: The answer [1,2,1] would also be accepted.

Example 2:

Output: [1,2,4]

Example 3:

Output: 

Constraints:

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

## Solution

Create a dummyHead and set dummyHead.next = head. Initialize temp = dummyHead. Each time delete zero sum consecutive nodes starting from temp.next. If there are nodes that are deleted, set temp.next to be the next node after deletion. Otherwise, set temp = temp.next.

Finally, return dummyHead.next.

• /**
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) { val = x; }
* }
*/
class Solution {
while (temp != null) {
ListNode zeroLast = removeZero(temp.next);
if (zeroLast == null)
temp = temp.next;
else
temp.next = zeroLast.next;
}
}

public ListNode removeZero(ListNode node) {
ListNode temp = node;
int sum = 0;
while (temp != null) {
sum += temp.val;
if (sum == 0)
return temp;
else
temp = temp.next;
}
return null;
}
}

• // OJ: https://leetcode.com/problems/remove-zero-sum-consecutive-nodes-from-linked-list/
// Time: O(N)
// Space: O(N)
class Solution {
public:
ListNode dummy;
unordered_map<int, ListNode*> m{ {0, &dummy} };
int sum = 0;
while (node) {
sum += node->val;
if (m.count(sum)) {
int s = sum;
for (auto p = m[sum]->next; p != node; p = p->next) {
s += p->val;
m.erase(s);
}
m[sum]->next = node->next;
if (m.count(sum)) {
} else {
m[sum] = node;
}
node = node->next;
}
return dummy.next;
}
};

• # Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
def removeZeroSumSublists(self, head: Optional[ListNode]) -> Optional[ListNode]:
last = {}
s, cur = 0, dummy
while cur:
s += cur.val
last[s] = cur
cur = cur.next
s, cur = 0, dummy
while cur:
s += cur.val
cur.next = last[s].next
cur = cur.next
return dummy.next

############

# 1171. Remove Zero Sum Consecutive Nodes from Linked List

# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
def removeZeroSumSublists(self, head: ListNode) -> ListNode:
prefix = 0
seen = {}
seen = dummy = ListNode(0)

prefix = 0

return dummy.next


• /**
* type ListNode struct {
*     Val int
*     Next *ListNode
* }
*/
last := map[int]*ListNode{}
cur := dummy
s := 0
for cur != nil {
s += cur.Val
last[s] = cur
cur = cur.Next
}
s = 0
cur = dummy
for cur != nil {
s += cur.Val
cur.Next = last[s].Next
cur = cur.Next
}
return dummy.Next
}

• /**
* class ListNode {
*     val: number
*     next: ListNode | null
*     constructor(val?: number, next?: ListNode | null) {
*         this.val = (val===undefined ? 0 : val)
*         this.next = (next===undefined ? null : next)
*     }
* }
*/

function removeZeroSumSublists(head: ListNode | null): ListNode | null {
const dummy = new ListNode(0, head);
const last = new Map<number, ListNode>();
let s = 0;
for (let cur = dummy; cur; cur = cur.next) {
s += cur.val;
last.set(s, cur);
}
s = 0;
for (let cur = dummy; cur; cur = cur.next) {
s += cur.val;
cur.next = last.get(s)!.next;
}
return dummy.next;
}