Add Solution for 082 Remove Duplicates from Sorted List II

cpp/082_Remove_Duplicates_from_Sorted_List_II.cpp

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+// 82. Remove Duplicates from Sorted List II
+/**
+ * Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.
+ * 
+ * For example,
+ * Given 1->2->3->3->4->4->5, return 1->2->5.
+ * Given 1->1->1->2->3, return 2->3.
+ * 
+ * Tags: Linked List
+ * 
+ * Author: Kuang Qin
+ */
+
+#include <iostream>
+
+using namespace std;
+
+/**
+ * Definition for singly-linked list.
+ */
+struct ListNode {
+    int val;
+    ListNode *next;
+    ListNode(int x) : val(x), next(NULL) {}
+    ListNode(int x, ListNode *p) : val(x), next(p) {}
+};
+
+class Solution {
+public:
+    ListNode* deleteDuplicates(ListNode* head) {
+        if (head == NULL || head->next == NULL) {
+            return head;
+        }
+
+        // dummy node to mark head position
+        ListNode dummy(0);
+        dummy.next = head;
+
+        ListNode *pre = &dummy, *curr = head;
+        while (curr != NULL) {
+            while (curr->next != NULL && curr->val == curr->next->val) {
+                curr = curr->next;
+            }
+
+            if (pre->next == curr) {    // curr has unique values
+                pre = curr;
+            }
+            else {  // curr to be deleted
+                pre->next = curr->next;
+            }
+
+            curr = curr->next;
+        }
+
+        return dummy.next;
+    }
+};
+
+// pointer to pointer
+class Solution_PP {
+public:
+    ListNode* deleteDuplicates(ListNode* head) {
+        if (head == NULL || head->next == NULL) {
+            return head;
+        }
+
+        // **pp to mark head position
+        ListNode **pp = &head;
+
+        while (*pp != NULL) {
+            ListNode *curr = *pp;
+            while (curr->next != NULL && curr->val == curr->next->val) {
+                curr = curr->next;
+            }
+
+            if (*pp == curr) {    // curr has unique values
+                pp = &(curr->next);
+            }
+            else {  // curr to be deleted
+                *pp = curr->next;
+            }
+        }
+
+        return head;
+    }
+};
+
+// recursive
+class Solution_Recursive {
+public:
+    ListNode* deleteDuplicates(ListNode* head) {
+        if (head == NULL || head->next == NULL) {
+            return head;
+        }
+
+        ListNode *next = head->next;
+        if (head->val != next->val) {   // head has unique values
+            head->next = deleteDuplicates(next);
+            return head;
+        }
+
+        // head to be deleted
+        while (next != NULL && head->val == next->val) {
+            next = next->next;
+        }
+
+        return deleteDuplicates(next);
+    }
+};
+
+int main() {
+    ListNode node5(3), node4(3, &node5), node3(3, &node4), node2(1, &node3), node1(1, &node2);
+    Solution sol;
+    ListNode *newhead = sol.deleteDuplicates(&node1);
+    for (ListNode *p = newhead; p != NULL; p = p->next) {
+        cout << p->val << " ";
+    }
+    cout << endl;
+    cin.get();
+
+    return 0;
+}