README_EN.md

2487. Remove Nodes From Linked List

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Description

You are given the head of a linked list.

Remove every node which has a node with a strictly 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

Solutions

Python3

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def removeNodes(self, head: Optional[ListNode]) -> Optional[ListNode]:
        nums = []
        while head:
            nums.append(head.val)
            head = head.next
        stk = []
        for v in nums:
            while stk and stk[-1] < v:
                stk.pop()
            stk.append(v)
        dummy = ListNode()
        head = dummy
        for v in stk:
            head.next = ListNode(v)
            head = head.next
        return dummy.next

Java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode removeNodes(ListNode head) {
        List<Integer> nums = new ArrayList<>();
        while (head != null) {
            nums.add(head.val);
            head = head.next;
        }
        Deque<Integer> stk = new ArrayDeque<>();
        for (int v : nums) {
            while (!stk.isEmpty() && stk.peek() < v) {
                stk.pop();
            }
            stk.push(v);
        }
        ListNode dummy = new ListNode();
        head = dummy;
        while (!stk.isEmpty()) {
            head.next = new ListNode(stk.pollLast());
            head = head.next;
        }
        return dummy.next;
    }
}

C++

/**
 * 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) {
        vector<int> nums;
        while (head) {
            nums.emplace_back(head->val);
            head = head->next;
        }
        vector<int> stk;
        for (int v : nums) {
            while (!stk.empty() && stk.back() < v) {
                stk.pop_back();
            }
            stk.push_back(v);
        }
        ListNode* dummy = new ListNode();
        head = dummy;
        for (int v : stk) {
            head->next = new ListNode(v);
            head = head->next;
        }
        return dummy->next;
    }
};

Go

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func removeNodes(head *ListNode) *ListNode {
	nums := []int{}
	for head != nil {
		nums = append(nums, head.Val)
		head = head.Next
	}
	stk := []int{}
	for _, v := range nums {
		for len(stk) > 0 && stk[len(stk)-1] < v {
			stk = stk[:len(stk)-1]
		}
		stk = append(stk, v)
	}
	dummy := &ListNode{}
	head = dummy
	for _, v := range stk {
		head.Next = &ListNode{Val: v}
		head = head.Next
	}
	return dummy.Next
}

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