diff --git a/dsa-solutions/lc-solutions/0000-0099/0082-remove-duplicates-from-sorted-list-2.md b/dsa-solutions/lc-solutions/0000-0099/0082-remove-duplicates-from-sorted-list-2.md new file mode 100644 index 000000000..16bb2b15b --- /dev/null +++ b/dsa-solutions/lc-solutions/0000-0099/0082-remove-duplicates-from-sorted-list-2.md @@ -0,0 +1,194 @@ +--- +id: remove-duplicates-from-sorted-list-2 +title: Remove Duplicates from Sorted List II (Leetcode) +sidebar_label: 0082-RemoveDuplicatesFromSortedListII +description: Given the head of a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list. Return the linked list sorted as well. +--- + +## Problem Description + +| Problem Statement | Solution Link | LeetCode Profile | +| :---------------- | :------------ | :--------------- | +| [Remove Duplicates from Sorted List II](https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/) | [Merge Two Sorted Lists Solution on LeetCode](https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/solutions) | [Aaradhya Singh ](https://leetcode.com/u/keira_09/) | + + +## Problem Description + +Given the head of a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list. Return the linked list sorted as well. + +### Examples + +#### Example 1 + +- **Input:** $head = [1,2,3,3,4,4,5]$ +- **Output:** $[1,2,5]$ + + +#### Example 2 + +- **Input:** $head = [1,1,1,2,3]$ +- **Output:** $[2,3]$ + + + +### Constraints + +- The number of nodes in the list is in the range [0, 300]. +- $-100 <= Node.val <= 100$ +- The list is guaranteed to be sorted in ascending order. + + +### Intuition + + +The goal is to remove all elements from a sorted linked list that have duplicate values, ensuring that each element appears only once. We use a dummy node to simplify handling edge cases and traverse the list, removing duplicates as we encounter them. + + +### Approach + +1. **Initialization:** + + - Create a dummy node to handle edge cases where the head itself might be a duplicate. + - Initialize two pointers, prev (starting at dummy) and curr (starting at head). + +2. **Traversal and Duplicate Removal:** + + - Traverse the linked list using the curr pointer. + - For each node, check if the current value matches the next node's value. + - If duplicates are detected, use a loop to skip all nodes with that value, deleting them. + - Update the prev pointer's next to point to the first non-duplicate node after the series of duplicates. + - If no duplicates are found, move both prev and curr pointers forward. + +3. **Completion:** + + - After the loop, update the head to point to the node after the dummy. + - Delete the dummy node to free memory. + Return the updated head of the linked list. + +### Solution Code + +#### Python + +```py +class ListNode: + def __init__(self, val=0, next=None): + self.val = val + self.next = next + +class Solution: + def deleteDuplicates(self, head: ListNode) -> ListNode: + if not head or not head.next: + return head + + dummy = ListNode(0) # Dummy node to handle the case when head is a duplicate + dummy.next = head + + prev = dummy + curr = head + + while curr and curr.next: + if prev.next.val == curr.next.val: + val = curr.next.val + while curr and curr.val == val: + temp = curr + curr = curr.next + del temp # Marking the node for garbage collection + prev.next = curr + else: + prev = prev.next + curr = curr.next + + head = dummy.next # Update head in case it has changed + del dummy # Marking the dummy node for garbage collection + return head +``` + +#### Java + +```java +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 deleteDuplicates(ListNode head) { + if (head == null || head.next == null) { + return head; + } + + ListNode dummy = new ListNode(0); // Dummy node to handle the case when head is a duplicate + dummy.next = head; + + ListNode prev = dummy; + ListNode curr = head; + + while (curr != null && curr.next != null) { + if (prev.next.val == curr.next.val) { + int val = curr.next.val; + while (curr != null && curr.val == val) { + ListNode temp = curr; + curr = curr.next; + temp = null; // Marking the node for garbage collection + } + prev.next = curr; + } else { + prev = prev.next; + curr = curr.next; + } + } + + head = dummy.next; // Update head in case it has changed + dummy = null; // Marking the dummy node for garbage collection + return head; + } +} +``` + +#### C++ + +```cpp +class Solution { +public: + ListNode* deleteDuplicates(ListNode* head) { + if (head == nullptr || head->next == nullptr) { + return head; + } + + ListNode* dummy = new ListNode(0); // Dummy node to handle the case when head is a duplicate + dummy->next = head; + + ListNode* prev = dummy; + ListNode* curr = head; + + while (curr != nullptr && curr->next != nullptr) + { + if (prev->next->val == curr->next->val) + { + int val = curr->next->val; + while (curr != nullptr && curr->val == val) + { + ListNode* temp = curr; + curr = curr->next; + delete temp; + } + prev->next = curr; + } else { + prev = prev->next; + curr = curr->next; + } + } + + head = dummy->next; // Update head in case it has changed + delete dummy; // Delete the dummy node + return head; + } +}; +``` + +### Conclusion + +The provided code effectively removes duplicates from a sorted linked list by iterating through the list and adjusting the pointers accordingly to skip duplicate nodes. It uses a dummy node to handle cases where the head itself is a duplicate and performs the deletion in place without modifying the values within the nodes. The solution has a time complexity of $O(n)$, where n is the number of nodes in the linked list, due to the linear traversal required to identify and remove duplicates. The space complexity is $O(1)$ since the algorithm operates in constant space, only using a few pointers and temporary variables regardless of the input size. Overall, this solution offers an efficient and straightforward approach to handling duplicate removal in a sorted linked list.