From 2f6299ac85609448c1171254f5cce547a3ff9ad3 Mon Sep 17 00:00:00 2001
From: Iurii Tatishchev <itatishch@gmail.com>
Date: Sun, 28 Apr 2024 12:38:23 -0700
Subject: [PATCH] 6.21 Lab: Doubly-Linked List (Insert - reject duplicates)

---
 04-dl-lists/StudentList.cpp | 46 +++++++++++--------------------------
 04-dl-lists/StudentList.h   |  5 ++--
 04-dl-lists/main.cpp        | 31 ++++++++++++-------------
 3 files changed, 31 insertions(+), 51 deletions(-)

diff --git a/04-dl-lists/StudentList.cpp b/04-dl-lists/StudentList.cpp
index 912d5db..820e1f7 100644
--- a/04-dl-lists/StudentList.cpp
+++ b/04-dl-lists/StudentList.cpp
@@ -72,10 +72,14 @@ void StudentList::displayListBack() const {
 }
 
 // **************************************************
-// The insertNode function inserts a node with
-// stu copied to its value member.
+// The insertNode function checks if a node with the
+// same key as dataIn's key is found in the list
+// If it is found, returns false, meaning that insert
+// has failed to add the new data (duplicate!)
+// otherwise inserts a node with
+// stu copied to its value member, and returns true.
 // **************************************************
-void StudentList::insertNode(Student dataIn) {
+bool StudentList::insertNode(Student dataIn) {
     ListNode *newNode;  // A new node
     ListNode *pCur;     // To traverse the list
 
@@ -91,6 +95,9 @@ void StudentList::insertNode(Student dataIn) {
         pCur = pCur->forw;
     }
 
+    // Return false early if the name is a duplicate
+    if (pCur->stu.name == dataIn.name) return false;
+
     // Insert the new node between pPre and pCur
     ListNode *pPre = pCur->back;     // The previous node
     pPre->forw = newNode;
@@ -101,38 +108,13 @@ void StudentList::insertNode(Student dataIn) {
 
     // Update the counter
     count++;
+
+    return true;
 }
 
 // **************************************************
-// The deleteNode function deletes a node with
-// the same key as its paramenter, if found
-// **************************************************
-bool StudentList::deleteNode(string target) {
-    ListNode *pCur;     // To traverse the list
-    bool success = false;
-
-    pCur = head->forw;
-    while (pCur != head && pCur->stu.name < target) {
-        pCur = pCur->forw;
-    }
-
-    if (pCur != head && pCur->stu.name == target) {
-        ListNode *pPrev = pCur->back;
-        ListNode *pNext = pCur->forw;
-        pPrev->forw = pNext;
-        pNext->back = pPrev;
-        delete pCur;
-        success = true;
-        count--;
-    }
-
-    return success;
-}
-
-
-// **************************************************
-// Destructor                                      *
-// This function deletes every node in the list.   *
+// Destructor
+// This function deletes every node in the list.
 // **************************************************
 StudentList::~StudentList() {
 
diff --git a/04-dl-lists/StudentList.h b/04-dl-lists/StudentList.h
index 0782110..59317ad 100644
--- a/04-dl-lists/StudentList.h
+++ b/04-dl-lists/StudentList.h
@@ -32,10 +32,9 @@ public:
     // Linked list operations
     int getCount() const { return count; }
 
-    void insertNode(Student);
-
-    bool deleteNode(std::string);
+    bool insertNode(Student);
 
+    // bool deleteNode(double);
     //void searchList() const;
     void displayListForw() const;
 
diff --git a/04-dl-lists/main.cpp b/04-dl-lists/main.cpp
index 00d78bd..0249173 100644
--- a/04-dl-lists/main.cpp
+++ b/04-dl-lists/main.cpp
@@ -2,16 +2,14 @@
 CIS 22C: Sorted Circular Doubly-Linked List with Sentinel Node
 
 This program:
-- Creates a sorted linked list (student name and gpa). The list is sorted in ascending order by name.
+- Creates a sorted linked list (student name and gpa). The list is sorted in ascending order by name. Assume name is a unique identifier.
 - Displays the list forwards(A to Z)
-- Deletes nodes from the list
 - Displays the list backwards(Z to A)
 
 Your task is to finish writing the following three functions:
-- default constructor (reuse code from your previous Lab)
-- insertNode()  (reuse code from your previous Lab)
-- displayListBack()  (reuse code from your previous Lab)
-- deleteNode()
+- default constructor (reuse code from your previous lab)
+- `displayListBack()`  (reuse code from your previous lab)
+- `insertNode()`  - change this function to reject duplicates. Assume `name` is a unique key.
 
  Written by: Iurii Tatishchev
  Reviewed by: Iurii Tatishchev
@@ -32,16 +30,18 @@ int main() {
     StudentList list;
 
     buildList(list); // insert data into the list
-    cout << "There are " << list.getCount() << " elements in the list." << endl;
+    cout << "The number of elements in the list is " << list.getCount() << "." << endl;
     string answer;
-    cout << "Delete [Y/N]? ";
-    getline(cin, answer);
+    cout << "Insert [Y/N]? ";
+    cin >> answer;
     if (answer == "Y" || answer == "y") {
-        string targetName;
-        cout << "Enter name to be removed from the list:" << endl;
-        getline(cin, targetName);
-        cout << targetName << (list.deleteNode(targetName) ? " - deleted!" : " - not found!") << endl;
-        cout << "There are " << list.getCount() << " elements in the list." << endl;
+        Student s;
+        cout << "Enter gpa then enter name:" << endl;
+        cin >> s.gpa >> s.name;
+        if (!list.insertNode(s)) {
+            cout << s.name << " - rejected: duplicate key!" << endl;
+        }
+        cout << "The number of elements in the list is " << list.getCount() << "." << endl;
     }
     cout << endl;
     list.displayListForw();
@@ -67,5 +67,4 @@ void buildList(StudentList &list) {
         list.insertNode(newStu);
         getline(cin, line);
     }
-
-}
\ No newline at end of file
+}