diff --git a/assignment1/problem1/Makefile b/assignment1/problem1/Makefile
new file mode 100644
index 0000000..779f6f5
--- /dev/null
+++ b/assignment1/problem1/Makefile
@@ -0,0 +1,5 @@
+EXEC = list
+SRC = $(wildcard *.c)
+
+$(EXEC): $(SRC)
+	gcc -o $@ $^ -Wall
diff --git a/assignment1/problem1/list.c b/assignment1/problem1/list.c
new file mode 100644
index 0000000..36ec53e
--- /dev/null
+++ b/assignment1/problem1/list.c
@@ -0,0 +1,195 @@
+/*
+ * Author: Walter
+ * Student ID: 1930006025
+ * Assignment_1_problem_1
+ */
+
+#include "list.h"
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+// Write all your functions here.
+bool IsEmpty(Node *head) {
+	if (head == NULL) {
+		return true;
+	} else {
+		return false;
+	}
+}
+
+/* code from pdf */
+Node *InsertNode(Node **phead, int index, double x) {
+	if (index < 0)
+		return NULL;
+	int currIndex = 1;
+	Node *currNode = *phead;
+	while (currNode != NULL && index > currIndex) {
+		currNode = currNode->next;
+		currIndex++;
+	}
+	if (index > 0 && currNode == NULL)
+		return NULL;
+	Node *newNode = (Node *)malloc(sizeof(Node));
+	newNode->data = x;
+	if (index == 0) {
+		newNode->next = *phead;
+		*phead = newNode;
+	} else {
+		newNode->next = currNode->next;
+		currNode->next = newNode;
+	}
+	return newNode;
+}
+
+int FindNode(Node *head, double x) {
+	int position;
+	Node *pnode;
+
+	/* position start from 1 */
+	for (pnode = head, position = 1; pnode; pnode = pnode->next, position++) {
+		if (pnode->data == x) {
+			return position;
+		}
+	}
+
+	return 0;
+}
+
+int DeleteNode(Node **phead, double x) {
+	/* position start from 1 */
+	int position;
+	Node *pnode;
+	Node *delNode;
+
+	/* if delete the first node */
+	if ((*phead)->data == x) {
+		delNode = *phead;
+		*phead = (*phead)->next;
+		free(delNode);
+		return 1;
+	}
+
+	/* if not the first node */
+	for (pnode = *phead, position = 2; pnode->next;
+			pnode = pnode->next, position++) {
+		/* loop for pnode->next->data == x */
+		if (pnode->next->data == x) {
+			/* delete node */
+			delNode = pnode->next;
+			pnode->next = pnode->next->next;
+			free(delNode);
+			return position;
+		}
+	}
+
+	/* if node not found, return 0 */
+	return 0;
+}
+
+void DisplayList(Node *head) {
+	Node *pnode;
+	/* loop for each node */
+	for (pnode = head; pnode; pnode = pnode->next) {
+		printf("%f ", pnode->data);
+	}
+	/* new line at the end */
+	printf("\n");
+}
+
+void DestroyList(Node *head) {
+	Node *pnode = head;
+	Node *delNode;
+	/* loop for each node */
+	while (pnode) {
+		/* store the tmp node */
+		delNode = pnode;
+		pnode = pnode->next;
+		free(delNode);
+	}
+}
+
+void InverstNode(Node **head) {
+	/* empty list */
+	if (*head == NULL) {
+		return;
+	}
+
+	/* only one node in list */
+	if ((*head)->next == NULL) {
+		return;
+	}
+
+	/* reverse Node */
+	Node *a, *b, *c;
+	a = NULL;
+	b = *head;
+	c = (*head)->next;
+
+	/* when c == NULL, b is the end of linked list */
+	while (c) {
+		/* reverse node */
+		b->next = a;
+		/* move a, b, c forward */
+		a = b;
+		b = c;
+		c = c->next;
+	}
+	/* finanl step */
+	b->next = a;
+	/* reset head */
+	*head = b;
+}
+
+void RemoveDuplicates(Node **head) {
+	Node *newHead = NULL, *currNode = *head;
+	double oldValue;
+	int position;
+
+	/* empty list, no need to do anything */
+	if ((*head) == NULL) {
+		return;
+	}
+
+	/* only one node in the list, no need to do anything */
+	if ((*head)->next == NULL) {
+		return;
+	}
+
+	/* loop until currNode point at NULL */
+	while (currNode) {
+		/* check whether there is any same value node after this node */
+		position = FindNode(currNode->next, currNode->data);
+
+		/* position is not 0, means this is the duplicated value */
+		if (position) {
+			/* record current duplicated value */
+			oldValue = currNode->data;
+
+			/* then use a for loop jump pass the duplicated value,
+			 * use for loop to check currNode is not NULL
+			 * before get currNode->data */
+			for (; currNode; currNode=currNode->next) {
+				/* exit when we find a new value */
+				if (currNode->data != oldValue) {
+					break;
+				}
+			}
+
+			continue;
+		}
+
+		/* if this is not a duplicated value,
+		 * add unique node to new linked list */
+		InsertNode(&newHead, 0, currNode->data);
+
+		/* move to next */
+		currNode = currNode->next;
+	}
+
+	/* Inverst to original direction */
+	InverstNode(&newHead);
+	/* reset head, remember to destory old list, avoid memory leak */
+	DestroyList(*head);
+	*head = newHead;
+}
diff --git a/assignment1/problem1/list.h b/assignment1/problem1/list.h
new file mode 100644
index 0000000..43c053a
--- /dev/null
+++ b/assignment1/problem1/list.h
@@ -0,0 +1,58 @@
+#ifndef MY_STACK
+#define MY_STACK
+
+#include <stdbool.h>
+
+typedef struct node {
+	double data;
+	struct node *next;
+} Node;
+
+/* function: tests whether a list is empty
+input: head: pointer to the first node
+output: true if the list is empty and false otherwise
+*/
+bool IsEmpty(Node *head);
+
+/* function: inserts a new node with certain data after a certain position
+input: phead: pointer to the pointer to the first node
+index: the new node is inserted after position index
+insert a new node as the head if index is 0
+x: data of the new node
+output: a pointer to the new node if insertion is successful, NULL otherwise
+*/
+Node *InsertNode(Node **phead, int index, double x);
+
+/* function: finds node with certain data
+input: head: pointer to the first node
+x: the first node whose data = x is returned
+output: returns the position of the first node whose data = x
+returns 0 if no such node exists
+*/
+int FindNode(Node *head, double x);
+
+/* function: deletes a node with certain data
+input: phead: pointer to the pointer to the first node
+x: the first node whose data = x is deleted
+output: returns the position of the deleted node
+returns 0 if no such node exists
+*/
+int DeleteNode(Node **phead, double x);
+
+/* function: prints all the nodes in the list
+input: head: pointer to the first node
+*/
+void DisplayList(Node *head);
+
+/* function: deletes all the nodes in the list and frees their memory
+input: head: pointer to the first node
+*/
+void DestroyList(Node *head);
+
+/* inverse a linked list */
+void InverstNode(Node **head);
+
+/* delete all duplicates node in a linked list */
+void RemoveDuplicates(Node **head);
+
+#endif
diff --git a/assignment1/problem1/test_main.c b/assignment1/problem1/test_main.c
new file mode 100644
index 0000000..dc2738b
--- /dev/null
+++ b/assignment1/problem1/test_main.c
@@ -0,0 +1,180 @@
+/* author: Walter
+ * Student_ID: 1930006025
+ * Assignment_problem_1
+ * This is a test unit file contain some test function and a main function to run it
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+
+#include "list.h"
+
+void test_inverse_empty_list();
+void test_inverse_one_list();
+void test_inverst_list();
+void test_remove_duplicate();
+
+int main() {
+	test_inverse_empty_list();
+	test_inverse_one_list();
+	test_inverst_list();
+	test_remove_duplicate();
+}
+
+void test_inverse_empty_list() {
+	Node *head = NULL;
+	printf("test_inverse_empty_list(): except 2 empty line:\n");
+	DisplayList(head);
+	InverstNode(&head);
+	DisplayList(head);
+}
+
+void test_inverse_one_list() {
+	Node *head = NULL;
+	printf("test_inverse_one_list(): except two same node:\n");
+	InsertNode(&head, 0, 39.0);
+	DisplayList(head);
+	InverstNode(&head);
+	DisplayList(head);
+	DestroyList(head);
+	head = NULL;
+}
+
+void test_inverst_list() {
+	Node *head = NULL;
+	printf("test_inverst_list(): except inverse list:\n");
+	for (int i=39; i<45; i++) {
+		InsertNode(&head, 0, (double)i);
+	}
+	DisplayList(head);
+	InverstNode(&head);
+	DisplayList(head);
+	DestroyList(head);
+	head = NULL;
+}
+
+/* four test cases from pdf */
+void test_remove_duplicate() {
+	Node *head = NULL;
+
+	printf("test_remove_duplicate(): except 1.0   4.0:\n");
+	InsertNode(&head, 0, 1.0);
+	InsertNode(&head, 1, 2.0);
+	InsertNode(&head, 2, 2.0);
+	InsertNode(&head, 3, 4.0);
+	InsertNode(&head, 4, 6.0);
+	InsertNode(&head, 5, 6.0);
+	DisplayList(head);
+	RemoveDuplicates(&head);
+	DisplayList(head);
+	DestroyList(head);
+	head = NULL;
+
+	printf("test_remove_duplicate(): except two empty line:\n");
+	head = NULL;
+	DisplayList(head);
+	RemoveDuplicates(&head);
+	DisplayList(head);
+	DestroyList(head);
+	head = NULL;
+
+	printf("test_remove_duplicate(): except empty line in result:\n");
+	head = NULL;
+	InsertNode(&head, 0, 6.0);
+	InsertNode(&head, 1, 6.0);
+	InsertNode(&head, 2, 6.0);
+	InsertNode(&head, 3, 7.0);
+	InsertNode(&head, 4, 7.0);
+	DisplayList(head);
+	RemoveDuplicates(&head);
+	DisplayList(head);
+	DestroyList(head);
+	head = NULL;
+	
+	printf("test_remove_duplicate(): except 6.0   7.0:\n");
+	head = NULL;
+	InsertNode(&head, 0, 6.0);
+	InsertNode(&head, 1, 7.0);
+	DisplayList(head);
+	RemoveDuplicates(&head);
+	DisplayList(head);
+	DestroyList(head);
+	head = NULL;
+	return;
+}
+
+
+/* old test function
+// Testing all the functions:
+int main(void) {
+	Node *head = NULL;
+
+	// Output: true
+	printf("%s\n", IsEmpty(head) ? "true" : "false");
+
+	// Must output an empty line:
+	DisplayList(head);
+
+	// Must output "insert failed":
+	Node *result = InsertNode(&head, 20, 7);
+	printf("%s\n", result == NULL ? "insert failed" : "insert succeeded");
+
+	// Output: 0.000000 1.000000 2.000000 3.000000 4.000000
+	for (int i = 0; i < 5; i++) {
+		InsertNode(&head, i, i);
+	}
+	DisplayList(head);
+
+	// Output: false
+	printf("%s\n", IsEmpty(head) ? "true" : "false");
+
+	// Output: 4.000000 3.000000 2.000000 1.000000 0.000000
+	// 0.000000 1.000000 2.000000 3.000000 4.000000
+	for (int i = 0; i < 5; i++) {
+		InsertNode(&head, 0, i);
+	}
+	DisplayList(head);
+
+	// Output: 0.000000 is at position 5
+	//         2.000000 is at position 3
+	//         4.000000 is at position 1
+	//         6.000000 is not in the list
+	for (int i = 0; i < 7; i += 2) {
+		int idx = FindNode(head, i);
+		if (idx > 0) {
+			printf("%f is at position %d\n", (double)i, idx);
+		} else {
+			printf("%f is not in the list\n", (double)i);
+		}
+	}
+
+	// Output: inserted 10.000000
+	//         4.000000 3.000000 2.000000 10.000000 1.000000 0.000000
+	//         0.000000 1.000000 2.000000 3.000000 4.000000
+	Node *in = InsertNode(&head, 3, 10);
+	printf("inserted %f\n", in->data);
+	DisplayList(head);
+
+	// Output: 4.000000 3.000000 2.000000 10.000000 1.000000
+	// 0.000000 1.000000 2.000000 3.000000 4.000000
+	//         3.000000 2.000000 10.000000 1.000000
+	//         0.000000 1.000000 2.000000 3.000000 4.000000
+	//         3.000000 2.000000 10.000000 1.000000
+	//         0.000000 1.000000 2.000000 3.000000
+	DeleteNode(&head, 0); // Delete in the middle of the list.
+	DisplayList(head);
+	DeleteNode(&head, 4); // Delete at the front of the list.
+	DisplayList(head);
+	DeleteNode(&head, 4); // Delete at the end of the list.
+	DisplayList(head);
+
+	printf("Reverse List ...\n");
+	InverstNode(&head);
+	DisplayList(head);
+
+	DestroyList(head);
+	head = NULL;
+
+	return 0;
+}
+*/