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2487. Remove Nodes From Linked List.cpp
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2487. Remove Nodes From Linked List.cpp
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// https://leetcode.com/problems/remove-nodes-from-linked-list/
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/
class Solution
{
public:
ListNode *removeNodes(ListNode *head)
{
ListNode *result = new ListNode();
vector<pair<int, int>> nodes;
stack<int> values;
unordered_set<int> positionsToRemove;
ListNode *current = head;
int i = 0;
while (current != nullptr)
{
nodes.push_back({current->val, i});
current = current->next;
i++;
}
for (int i = nodes.size() - 1; i >= 0; --i)
{
while (!values.empty() && values.top() <= nodes[i].first)
values.pop();
if (!values.empty())
positionsToRemove.insert(nodes[i].second);
values.push(nodes[i].first);
}
current = result;
for (int i = 0; i < nodes.size(); ++i)
{
if (positionsToRemove.find(nodes[i].second) == positionsToRemove.end())
{
current->next = new ListNode(nodes[i].first);
current = current->next;
}
}
return result->next;
}
};