diff --git a/labs/cs2106/labs/lab4/linkedlist/pb/bintree.c b/labs/cs2106/labs/lab4/linkedlist/pb/bintree.c
new file mode 100644
index 0000000..0365c92
--- /dev/null
+++ b/labs/cs2106/labs/lab4/linkedlist/pb/bintree.c
@@ -0,0 +1,192 @@
+#include "bintree.h"
+#include "mymalloc.h"
+#include <stdio.h>
+#include <stdlib.h>
+
+/* ------------------------- DO NOT IMPLEMENT THESE ----------------------
+
+These are provided "free" to you, and you do not need to implement them,
+though you MAY  need to understand what they do. Some give you hints
+on how to work with pointers to pointers. You MAY find some of these
+functions useful.
+
+  ------------------------------------------------------------------------- */
+
+// Searches for the node containing "name" in the tree whose root is at "root",
+// returning both the node ifself in "node", and its parent in "prevnode"
+// (useful for deleting node). Both "node" and "prevnode" are set to NULL
+// if name is not found in the tree.
+
+void findNode(char *name, TTreeNode *root, TTreeNode **node,
+              TTreeNode **prevnode) {
+
+  TTreeNode *trav = root;
+  TTreeNode *prev = NULL;
+
+  while (trav != NULL) {
+    int cmp = strcmp(trav->name, name);
+
+    if (cmp == 0) {
+      *node = trav;
+      *prevnode = prev;
+      return;
+    }
+
+    prev = trav;
+    if (cmp < 0)
+      trav = trav->right;
+    else
+      trav = trav->left;
+  }
+
+  *node = NULL;
+  *prevnode = NULL;
+}
+
+// Searches for the node with the smallest value ("smallest node") in the tree
+// originating at "node". Returns the smallest node and its parent in
+// "smallest_node" and "parent" respectively.
+void findSmallest(TTreeNode *node, TTreeNode **smallest_node,
+                  TTreeNode **parent) {
+  TTreeNode *trav = node;
+  TTreeNode *prev = NULL;
+
+  if (trav == NULL)
+    return;
+
+  while (trav->left != NULL) {
+    prev = trav;
+    trav = trav->left;
+  }
+
+  *smallest_node = trav;
+  *parent = prev;
+}
+
+// Delete a node at "node" with parent node "prevnode"
+void delNode(TTreeNode *node, TTreeNode *prevnode) {
+  // This is a leaf node
+  if (node->left == NULL && node->right == NULL) {
+    // See whether node is on parent's left or right, and NULL the
+    // corresponding pointer
+
+    int cmp = strcmp(prevnode->name, node->name);
+
+    // Previous node is smaller than this one. This
+    // node is on the right
+    if (cmp < 0)
+      prevnode->right = NULL;
+    else
+      prevnode->left = NULL;
+
+    freenode(node);
+
+    return;
+  }
+
+  // This has a child on the left only
+  if (node->right == NULL) {
+    // Copy the right child over
+    node = node->left;
+    freenode(node->left);
+    return;
+  }
+
+  // This has a child on the right only
+  if (node->left == NULL) {
+    node = node->right;
+    freenode(node->right);
+    return;
+  }
+
+  // This has children on both nodes
+  TTreeNode *smallest, *smallest_parent;
+  findSmallest(node->right, &smallest, &smallest_parent);
+  node = smallest;
+  smallest_parent->left = NULL;
+  freenode(smallest);
+}
+
+/* ---------------------------- IMPLEMENT THESE --------------------------- */
+
+// Create a new node with name set to "name" and
+// phoneNum set to "phoneNum".
+void delTree(TTreeNode *root) {
+  // Implement deleting the entire tree, whose
+  // root is at "root".
+  if (root == NULL)
+    return;
+  if (root->left != NULL)
+    delTree(root->left);
+  if (root->right != NULL)
+    delTree(root->right);
+  freenode(root);
+}
+
+TTreeNode *makeNewNode(char *name, char *phoneNum) {
+  TTreeNode *node = mymalloc(sizeof(TTreeNode));
+  node->name = mymalloc(strlen(name) + 1);
+  strcpy(node->name, name);
+  strcpy(node->phoneNum, phoneNum);
+  node->left = NULL;
+  node->right = NULL;
+  return node;
+  // Implement makeNewNode to create a new
+  // TTreeNode containing name and phoneNum
+}
+
+// Add a new node to the tree.
+// Note that "root" is a POINTER to the tree's root,
+// not the root itself.
+
+void addNode(TTreeNode **root, TTreeNode *node) {
+  if (*root == NULL) {
+    *root = node;
+  }
+
+  TTreeNode **trav = root;
+
+  while (1) {
+
+    int cmp = strcmp((*trav)->name, node->name);
+    if (cmp == 0)
+      return;
+    if (cmp > 0) {
+      if ((*trav)->left == NULL)
+        (*trav)->left = node;
+      else {
+        trav = &((*trav)->left);
+        continue;
+      }
+    } else if (cmp < 0) {
+      if ((*trav)->right == NULL)
+        (*trav)->right = node;
+      else {
+        trav = &((*trav)->right);
+        continue;
+      }
+    }
+  }
+
+  // Add a new node to the tree, where root is
+  // the POINTER to the tree's root.
+}
+
+void freenode(TTreeNode *node) {
+  myfree(node->name);
+  myfree(node);
+  // Frees the memory used by node.
+}
+
+void print_inorder(TTreeNode *node) {
+  // Implement in-order printing of the tree
+  // Recursion is probably best here.
+
+  if (node == NULL)
+    return;
+  if (node->left != NULL)
+    print_inorder(node->left);
+  printf("Name is %s  Number is %s\n", node->name, node->phoneNum);
+  if (node->right != NULL)
+    print_inorder(node->right);
+}
diff --git a/labs/cs2106/labs/lab4/linkedlist/pb/bintree.h b/labs/cs2106/labs/lab4/linkedlist/pb/bintree.h
new file mode 100644
index 0000000..7f4744d
--- /dev/null
+++ b/labs/cs2106/labs/lab4/linkedlist/pb/bintree.h
@@ -0,0 +1,17 @@
+#include <string.h>
+#include <stdlib.h>
+
+typedef struct tn {
+    char *name;
+    char phoneNum[9];
+    struct tn *left, *right;
+} TTreeNode;
+
+void findNode(char *, TTreeNode *, TTreeNode **, TTreeNode **);
+void findSmallest(TTreeNode *, TTreeNode **, TTreeNode **);
+void delNode(TTreeNode *, TTreeNode *);
+void delTree(TTreeNode *);
+TTreeNode *makeNewNode(char *, char *);
+void addNode(TTreeNode **, TTreeNode *);
+void freenode(TTreeNode *);
+void print_inorder(TTreeNode *);
diff --git a/labs/cs2106/labs/lab4/linkedlist/pb/llist.c b/labs/cs2106/labs/lab4/linkedlist/pb/llist.c
new file mode 100644
index 0000000..22398a9
--- /dev/null
+++ b/labs/cs2106/labs/lab4/linkedlist/pb/llist.c
@@ -0,0 +1,239 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdarg.h>
+
+#include "llist.h"
+
+//#define DEBUG       // Enable debug printing
+
+// Debug printer
+
+void dbprintf(char *format, ...) {
+#ifdef DEBUG
+    va_list args;
+
+    va_start(args, format);
+    vprintf(format, args);
+#endif
+}
+
+// Implements a double linked list.
+
+// Create a new node. You need to
+// Create your own TData node, populate
+// it, then create a new node with a suitable
+// key. Insertion into the link list is
+// by ascending order of the key. An example key
+// might be the starting address of a memory segment.
+
+TNode *make_node(unsigned int key, TData *data) {
+    TNode *node = malloc(sizeof(TNode));
+    node->key = key;
+    node->pdata = data;
+    node->prev = NULL;
+    node->next = NULL;
+
+    return node;
+}
+
+// Inserts a node into the correct point of the
+// double linked list. The list is sorted
+// in ascending order of the key. Duplicate keys
+// are permitted, though not recommended.
+// llist = Pointer to link list
+// node = Pointer to node created by make_node
+// dir = 0: Insert in ascending order
+// dir = 1: Insert in descending order
+
+void insert_node(TNode **llist, TNode *node, int dir) {
+    if(*llist == NULL) {
+        *llist = node;
+        (*llist)->trav = *llist;
+        (*llist)->tail = *llist;
+    }
+    else 
+        if(((*llist)->key >= node->key && dir == 0) || (((*llist)->key <= node->key) && dir == 1)) {
+            node->next = *llist;
+            (*llist)->prev = node;
+            *llist = node;
+            (*llist)->trav = *llist;
+        }
+        else
+        {
+            TNode *trav = *llist;
+
+            if(dir == 0)
+                while(trav->next != NULL && trav->key < node->key) 
+                    trav = trav->next;
+            else if(dir == 1)
+                while(trav->next != NULL && trav->key > node->key)
+                    trav = trav->next;
+
+            if(trav->next == NULL && ((trav->key < node->key && dir == 0) || 
+                        (trav->key > node->key && dir == 1))) {
+                trav->next = node;
+                node->prev = trav;
+
+                // Set the tail
+                (*llist)->tail = node;
+            } else {
+                // Insert into the previous space
+
+                node->next = trav;
+
+                if(trav->prev != NULL) {
+                    trav->prev->next = node;
+                    node->prev = trav->prev;
+                }
+
+                if(trav->next != NULL) {
+                }
+
+                trav->prev = node;
+            }
+        }
+}
+
+// Remove a given node from the linked list
+void delete_node(TNode **llist, TNode *node) {
+
+    if(*llist == NULL || node == NULL)
+        return;
+
+    if((*llist)->key == node->key) {
+        // Node to be deleted is at the front of the list.
+        *llist = (*llist)->next;
+
+        // Ensure that we don't point to it anymore.
+        if(*llist != NULL)
+            (*llist)->prev = NULL;
+    }
+    else
+    {
+        TNode *trav = *llist;
+
+        while(trav != NULL && trav->key != node->key) 
+            trav = trav->next;
+
+        // We've found the deletion point
+        if(trav != NULL) {
+            trav->prev->next = trav->next;
+
+            if(trav->next != NULL) 
+                trav->next->prev = trav->prev;
+            else
+                (*llist)->tail = trav->prev;
+        }
+
+    }
+
+    free(node);
+}
+
+// Find a node that has the value of key
+// If there are duplicate keys, the first one encountered
+// will be returned.
+TNode *find_node(TNode *llist, unsigned int key) {
+    if(llist == NULL)
+        return NULL;
+
+    TNode *trav = llist;
+
+    while(trav != NULL && trav->key != key)
+        trav = trav->next;
+
+    return trav;
+}
+
+// Merge the node provided with either the node after or the node before.
+// You need to manage merging the data in node->pdata yourself. This code just
+// deletes the larger of the two nodes.
+// dir = 0: Merge with node before
+// dir = 1: Merge with node after
+
+void merge_node(TNode *llist, TNode *node, int dir) {
+    if(dir == 0) {
+        if(node->prev == NULL)
+            return;
+
+        delete_node(&llist, node);
+    }
+    else 
+        if(dir == 1) {
+            if(node->next == NULL)
+                return;
+
+            delete_node(&llist, node->next);
+        }
+}
+
+// Go over every element of llist, and call func
+// func prototype is void func(TNode *);
+
+void process_list(TNode *llist, void (*func)(TNode *)) {
+    TNode *trav = llist;
+    while(trav) {
+        func(trav);
+        trav = trav->next;
+    }
+
+}
+
+
+// Purge the entire list. You must
+// free any dynamic data in the TData
+// struct yourself.
+void purge_list(TNode **llist) {
+    TNode *trav = *llist, *tmp;
+    while(trav) {
+        tmp = trav->next;
+        free(trav);
+        trav = tmp;
+    }
+
+    *llist = NULL;
+}
+
+
+// Reset traverser
+// where=0 START: Resets traverser to start of list
+// where=1 END: Rsets
+void reset_traverser(TNode *llist, int where)
+{
+    if(llist == NULL)
+        return;
+
+    if(where == FRONT)
+        llist->trav = llist;
+    else
+        if(where == REAR)
+            llist->trav = llist->tail;
+}
+
+// Get the next node
+TNode *succ(TNode *llist)
+{
+    if(llist == NULL)
+        return NULL;
+
+    TNode *ret = llist->trav;
+
+    if(llist->trav != NULL)
+        llist->trav = llist->trav->next;
+
+    return ret;
+}
+
+// Get the previous node
+TNode *pred(TNode *llist)
+{
+    if(llist == NULL)
+        return NULL;
+
+    TNode *ret = llist->trav;
+
+    if(llist->trav != NULL)
+        llist->trav = llist->trav->prev;
+
+    return ret;
+}
diff --git a/labs/cs2106/labs/lab4/linkedlist/pb/llist.h b/labs/cs2106/labs/lab4/linkedlist/pb/llist.h
new file mode 100644
index 0000000..23624a9
--- /dev/null
+++ b/labs/cs2106/labs/lab4/linkedlist/pb/llist.h
@@ -0,0 +1,115 @@
+#include <stdbool.h>
+#include <stdio.h>
+
+// Uncomment the next line to enable debug printing
+#define DEBUG // Enable debug printing
+
+// The debug printer; used like a normal printf, except
+// that printing can be turned off by commenting out the
+// #define DEBUG above.
+void dbprintf(char *format, ...);
+
+// You should modify this structure to hold
+// whatever you need to implement your
+// memory manager. You can delete the
+// val field. It is only used for testlist.c
+
+typedef struct td {
+  bool occupied;
+  size_t size;
+} TData;
+
+/* -----------------------------------------
+   BASIC ROUTINES
+
+   Basic linked list routines
+
+   ---------------------------------------- */
+
+// Basic double linked list node.
+
+typedef struct tn {
+  unsigned int key;
+  TData *pdata; // Pointer to the data you want to store
+
+  struct tn *trav; // Only used in the root for traversal
+  struct tn *tail; // Only used in the root for finding the end of the list
+  struct tn *prev;
+  struct tn *next;
+} TNode;
+
+// Insert Direction
+#define ASCENDING 0
+#define DESCENDING 1
+
+// Merge direction
+#define PRECEDING 0
+#define SUCCEEDING 1
+
+// Traverser position
+#define FRONT 0
+#define REAR 1
+
+// Create a new node. You need to
+// Create your own TData node, populate
+// it, then create a new node with a suitable
+// key. Insertion into the link list is
+// by ascending order of the key. An example key
+// might be the starting address of a memory segment.
+
+TNode *make_node(unsigned int key, TData *data);
+
+// Inserts a node into the correct point of the
+// double linked list. The list is sorted
+// in ascending order of the key. Duplicate keys
+// are permitted, though not recommended.
+// llist = Pointer to link list
+// node = Pointer to node created by make_node
+// dir = 0: Insert in ascending order
+// dir = 1: Insert in descending order
+
+void insert_node(TNode **llist, TNode *node, int dir);
+
+// Remove a given node from the linked list
+void delete_node(TNode **llist, TNode *node);
+
+// Find a node that has the value of key
+// If there are duplicate keys, the first one encountered
+// will be returned.
+TNode *find_node(TNode *llist, unsigned int key);
+
+// Merge the node provided with either the node after or the node before.
+// You need to manage merging the data in node->pdata yourself. This code just
+// deletes the larger of the two nodes.
+// dir = 0: Merge with node before
+// dir = 1: Merge with node after
+
+void merge_node(TNode *llist, TNode *node, int dir);
+
+// Purge the entire list. You must
+// free any dynamic data in the TData
+// struct yourself.
+void purge_list(TNode **llist);
+
+/* -----------------------------------------
+   TRAVERSAL ROUTINES
+
+   Lets you traverse the linked list
+
+   ---------------------------------------- */
+
+// Go over every element of llist, and call func
+// func prototype is void func(TNode *);
+
+void process_list(TNode *llist, void (*func)(TNode *));
+
+// Reset traverser
+// where=0 START: Resets traverser to start of list
+// where=1 END: Rsets
+void reset_traverser(TNode *llist, int where);
+
+// Get the next node
+TNode *succ(TNode *llist);
+
+// Get the previous node
+TNode *pred(TNode *llist);
diff --git a/labs/cs2106/labs/lab4/linkedlist/pb/mymalloc.c b/labs/cs2106/labs/lab4/linkedlist/pb/mymalloc.c
new file mode 100644
index 0000000..f4e0366
--- /dev/null
+++ b/labs/cs2106/labs/lab4/linkedlist/pb/mymalloc.c
@@ -0,0 +1,103 @@
+#include "mymalloc.h"
+
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/_types/_null.h>
+
+#include "llist.h"
+
+char _heap[MEMSIZE] = {0};
+TNode *_memlist = NULL; // To maintain information about length
+
+// Do not change this. Used by the test harness.
+// You may however use this function in your code if necessary.
+long get_index(void *ptr) {
+  if (ptr == NULL)
+    return -1;
+  else
+    return (long)((char *)ptr - &_heap[0]);
+}
+
+// Allocates size bytes of memory and returns a pointer
+// to the first byte.
+void *mymalloc(size_t size) {
+  if (_memlist == NULL) {
+    TData *data = malloc(sizeof(TData));
+    data->occupied = false;
+    data->size = MEMSIZE;
+    _memlist = make_node(0, data);
+  }
+
+  // loop through the list to find a free block
+  // if found, split the block and return the pointer
+  // if not found, return NULL
+  TNode *curr = _memlist;
+  TNode *best = NULL;
+  while (curr != NULL) {
+    if (curr->pdata->occupied == true) {
+      curr = curr->next;
+      continue;
+    }
+    if (curr->pdata->size < size) {
+      curr = curr->next;
+      continue;
+    }
+    if (best == NULL) {
+      best = curr;
+      curr = curr->next;
+      continue;
+    }
+    if (best->pdata->size > curr->pdata->size) {
+      best = curr;
+      curr = curr->next;
+      continue;
+    }
+    curr = curr->next;
+  }
+  if (best == NULL)
+    return NULL;
+  best->pdata->occupied = true;
+  if (best->pdata->size > size) {
+    // 	Create a new node with the leftover space
+    TData *newData = malloc(sizeof(TData));
+    newData->occupied = false;
+    newData->size = best->pdata->size - size;
+    TNode *newNode = make_node(best->key + size, newData);
+    // insert new node after the current one in the list.
+    insert_node(&_memlist, newNode, 0);
+    // change the size of the current node.
+    best->pdata->size = size;
+  }
+  return &_heap[best->key];
+}
+
+// Frees memory pointer to by ptr.
+void myfree(void *ptr) {
+  if (ptr == NULL)
+    return;
+  long index = get_index(ptr);
+  TNode *node = find_node(_memlist, index);
+  if (node == NULL)
+    return;
+  node->pdata->occupied = false;
+  // merge with the next node if it is free
+  while (node->next != NULL && node->next->pdata->occupied == false) {
+    node->pdata->size += node->next->pdata->size;
+    merge_node(_memlist, node, 1);
+  }
+
+  while (node->prev != NULL && node->prev->pdata->occupied == false) {
+    TNode *prev = node->prev;
+    prev->pdata->size += node->pdata->size;
+    merge_node(_memlist, node, 0);
+  }
+}
+
+void print_node(TNode *node) {
+  printf("Status: %s Start index: %d Length: %zu\n",
+         node->pdata->occupied ? "ALLOCATED" : "FREE", node->key,
+         node->pdata->size);
+}
+
+void print_memlist() { process_list(_memlist, print_node); }
diff --git a/labs/cs2106/labs/lab4/linkedlist/pb/mymalloc.h b/labs/cs2106/labs/lab4/linkedlist/pb/mymalloc.h
new file mode 100644
index 0000000..9fe7bac
--- /dev/null
+++ b/labs/cs2106/labs/lab4/linkedlist/pb/mymalloc.h
@@ -0,0 +1,7 @@
+#include <stdio.h>
+#define MEMSIZE 64 * 1024 // Size of memory in bytes
+
+long get_index(void *ptr);
+void print_memlist();
+void *mymalloc(size_t);
+void myfree(void *);
diff --git a/labs/cs2106/labs/lab4/linkedlist/pb/phonebook.c b/labs/cs2106/labs/lab4/linkedlist/pb/phonebook.c
new file mode 100644
index 0000000..8b58851
--- /dev/null
+++ b/labs/cs2106/labs/lab4/linkedlist/pb/phonebook.c
@@ -0,0 +1,51 @@
+#include <stdio.h>
+#include "phonebook.h"
+#include "bintree.h"
+
+static TTreeNode *_root = NULL;
+
+char *findPerson(char *name)
+{
+    TTreeNode *node, *prev;
+    findNode(name, _root, &node, &prev);
+
+    if (node != NULL)
+        return node->phoneNum;
+    else
+        return NULL;
+}
+
+void print_phonebook()
+{
+    print_inorder(_root);
+}
+
+void addPerson(char *name, char *phoneNum)
+{
+    if (findPerson(name) == NULL)
+    {
+        TTreeNode *node = makeNewNode(name, phoneNum);
+        addNode(&_root, node);
+    }
+    else
+        printf("%s is already in phonebook.\n", name);
+}
+
+void delPerson(char *name)
+{
+    TTreeNode *node, *prevnode;
+    findNode(name, _root, &node, &prevnode);
+    if (node == NULL)
+    {
+        printf("Unable to find %s\n", name);
+        return;
+    }
+
+    delNode(node, prevnode);
+}
+
+void delPhonebook()
+{
+    delTree(_root);
+    _root = NULL;
+}
diff --git a/labs/cs2106/labs/lab4/linkedlist/pb/phonebook.h b/labs/cs2106/labs/lab4/linkedlist/pb/phonebook.h
new file mode 100644
index 0000000..539cd43
--- /dev/null
+++ b/labs/cs2106/labs/lab4/linkedlist/pb/phonebook.h
@@ -0,0 +1,5 @@
+char *findPerson(char *);
+void addPerson(char *, char *);
+void delPerson(char *);
+void print_phonebook();
+void delPhonebook();
diff --git a/labs/cs2106/labs/lab4/linkedlist/pb/testpb.c b/labs/cs2106/labs/lab4/linkedlist/pb/testpb.c
new file mode 100644
index 0000000..5a85e56
--- /dev/null
+++ b/labs/cs2106/labs/lab4/linkedlist/pb/testpb.c
@@ -0,0 +1,60 @@
+#include <stdio.h>
+#include "phonebook.h"
+
+#define ITEMS 5
+
+typedef struct d
+{
+    char *name, *tel;
+} TData;
+
+void printResult(char *name)
+{
+    char *result;
+
+    printf("Looking for %s ", name);
+    result = findPerson(name);
+    if (result == NULL)
+        printf("NOT FOUND\n");
+    else
+        printf(" Number is %s\n", result);
+}
+
+int main()
+{
+    TData data[ITEMS] = {{"Fred Astaire", "95551234"}, {"Jean Valjean", "95558764"}, {"Gal Gadot", "95551123"}, {"Aiken Dueet", "95558876"}, {"Victor Hugo", "95524601"}};
+
+    int i;
+
+    for (i = 0; i < ITEMS; i++)
+    {
+        printf("Adding %s, phone number %s\n", data[i].name, data[i].tel);
+        addPerson(data[i].name, data[i].tel);
+    }
+
+    printf("\nNow retrieiving stored data.\n");
+    char *result;
+
+    for (i = 0; i < ITEMS; i++)
+    {
+        printResult(data[i].name);
+    }
+
+    printf("\nRetrieving unknown person.\n");
+    printResult("Wee Tu Loh");
+
+    printf("\nPrinting entire phonebook.\n");
+    print_phonebook();
+
+    printf("\nDeleting Aiken Dueet.\n");
+    delPerson("Aiken Dueet");
+    print_phonebook();
+
+    printf("\nDeleting Victor Hugo.\n");
+    delPerson("Victor Hugo");
+    print_phonebook();
+
+    printf("\nDeleting entire phone book.\n");
+    delPhonebook();
+    print_phonebook();
+}