Today I have done leetcode's May LeetCoding Challenge with cpp.

May LeetCoding Challenge 6

Description

Remove Nodes From Linked List

You are given the head of a linked list.

Remove every node which has a node with a greater value anywhere to the right side of it.

Return the head of the modified linked list.

Example 1:

Input: head = [5,2,13,3,8]
Output: [13,8]
Explanation: The nodes that should be removed are 5, 2 and 3.
- Node 13 is to the right of node 5.
- Node 13 is to the right of node 2.
- Node 8 is to the right of node 3.

Example 2:

Input: head = [1,1,1,1]
Output: [1,1,1,1]
Explanation: Every node has value 1, so no nodes are removed.

Constraints:

• The number of the nodes in the given list is in the range [1, 105].
• 1 <= Node.val <= 105

Solution

class Solution {
public:
  ListNode* removeNodes(ListNode* head) {
    stack<ListNode*> st;
    while(head) {
      while(st.size() && st.top()->val < head->val) {
        st.pop();
      }
      st.push(head);
      head = head->next;
    }
    ListNode *current = st.top();
    current->next = nullptr;
    st.pop();
    while(st.size()) {
      st.top()->next = current;
      current = st.top();
      st.pop();
      
    }
    return current;
  }
};