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Remove Zero Sum Consecutive Nodes from Linked List in C++
Suppose we have given the head of a linked list; we have to repeatedly delete consecutive sequences of nodes that sum to 0 until there are no such sequences. So after doing so, we have to return the head of the final linked list. So if the list is like [1,2,-3,3,1], then the result will be [3,1].
To solve this, we will follow these steps −
Create a node called dummy, and store 0 into it, set next of dummy := head
create one map m, store dummy for the key 0 into m, set sum = 0
while head is not null −
sum := sum + value of head, set m[sum] := head, and head := next of head
head := dummy
sum := 0
while head is not null
sum := sum + value of head
temp := m[sum]
if temp is not head, then next of head := next of temp
head := next of head
return next of dummy
Let us see the following implementation to get better understanding −
Example
#include <bits/stdc++.h>
using namespace std;
class ListNode{
public:
int val;
ListNode *next;
ListNode(int data){
val = data;
next = NULL;
}
};
ListNode *make_list(vector<int> v){
ListNode *head = new ListNode(v[0]);
for(int i = 1; i<v.size(); i++){
ListNode *ptr = head;
while(ptr->next != NULL){
ptr = ptr->next;
}
ptr->next = new ListNode(v[i]);
}
return head;
}
void print_list(ListNode *head){
ListNode *ptr = head;
cout << "[";
while(ptr){
cout << ptr->val << ", ";
ptr = ptr->next;
}
cout << "]" << endl;
}
class Solution {
public:
ListNode* removeZeroSumSublists(ListNode* head) {
ListNode* dummy = new ListNode(0);
dummy->next = head;
unordered_map <int, ListNode*> m;
m[0] = dummy;
int sum = 0;
while(head){
sum += head->val;
m[sum] = head;
head = head->next;
}
head = dummy;
sum = 0;
while(head){
sum += head->val;
ListNode* temp = m[sum];
if(temp != head){
head->next = temp->next;
}
head = head->next;
}
return dummy->next;
}
};
main(){
vector<int> v1 = {1,2,-3,3,1};
ListNode *head = make_list(v1);
Solution ob;
print_list(ob.removeZeroSumSublists(head));
}Input
[1,2,-3,3,1]
Output
[3,1]
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