02.01. Remove Duplicate Node

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def removeDuplicateNodes(self, head: ListNode) -> ListNode:
        if head is None or head.next is None:
            return head
        cache = set()
        cache.add(head.val)
        cur, p = head, head.next
        while p:
            if p.val not in cache:
                cur.next = p
                cur = cur.next
                cache.add(p.val)
            p = p.next
        cur.next = None
        return head

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode removeDuplicateNodes(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        Set<Integer> s = new HashSet<>();
        s.add(head.val);
        ListNode cur = head;
        for (ListNode p = head.next; p != null; p = p.next) {
            if (!s.contains(p.val)) {
                cur.next = p;
                cur = cur.next;
                s.add(p.val);
            }
        }
        cur.next = null;
        return head;
    }
}

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var removeDuplicateNodes = function (head) {
    if (head == null || head.next == null) return head;
    const cache = new Set([]);
    cache.add(head.val);
    let cur = head,
        fast = head.next;
    while (fast !== null) {
        if (!cache.has(fast.val)) {
            cur.next = fast;
            cur = cur.next;
            cache.add(fast.val);
        }
        fast = fast.next;
    }
    cur.next = null;
    return head;
};

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* removeDuplicateNodes(ListNode* head) {
        if (head == nullptr || head->next == nullptr) {
            return head;
        }
        unordered_set<int> cache = {head->val};
        ListNode *cur = head;
        for (ListNode *p = head->next; p != nullptr; p = p->next) {
            if (!cache.count(p->val)) {
                cur->next = p;
                cur = cur->next;
                cache.insert(p->val);
            }
        }
        cur->next = nullptr;
        return head;
    }
};

func removeDuplicateNodes(head *ListNode) *ListNode {
	if head == nil {
		return nil
	}
	vis := map[int]bool{head.Val: true}
	p := head
	for p.Next != nil {
		if vis[p.Next.Val] {
			p.Next = p.Next.Next
		} else {
			vis[p.Next.Val] = true
			p = p.Next
		}
	}
	return head
}