diff --git a/semester2/challenge1/main.c b/semester2/challenge1/main.c
new file mode 100644
index 0000000..102fa4b
--- /dev/null
+++ b/semester2/challenge1/main.c
@@ -0,0 +1,194 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+#define NUM_USERS 611
+#define NUM_MOVIES 9743
+#define NUM_GENRES 20
+
+typedef struct Movies
+{
+    int movieID;
+    struct Movies *next;
+} Movies;
+
+typedef struct Genres
+{
+    int genreID;
+    struct Genres *next;
+} Genres;
+
+//输入电影风格返回其映射的id
+int movie_style_map(char *style)
+{
+
+    int index = 0;
+    const char *movies[] = {"Action", "Adventure", "Animation", "Children's",
+                            "Comedy", "Crime", "Documentary", "Drama",
+                            "Fantasy", "Film-Noir", "Horror", "IMAX", "Musical",
+                            "Mystery", "Romance", "Sci-Fi", "Thriller",
+                            "War", "Western"};
+
+    while (strcmp(movies[index], style) != 0)
+    {
+        index++;
+    }
+    return index;
+}
+
+// 函数原型
+Movies *appendMovies(Movies *last, int id);
+int getGenreID(int movieID, Genres ** movies); // 传入movieID,输出风格下标
+void clearArrInt(int* arr, int size); // 将所有元素设为0
+
+int main(void)
+{
+    // Firstly open the ratings.csv
+    FILE *fp;
+    fp = fopen("./ratings.csv", "r");
+
+    char *buf = malloc(256 * sizeof(char));
+
+    // Declare the users table and init with null.
+    Movies *users[NUM_USERS];
+    for (int i = 0; i < NUM_USERS; i++)
+    {
+        users[i] = NULL;
+    }
+
+    fgets(buf, 256 * sizeof(char), fp);
+
+    // 看每个用户喜欢什么电影
+    int userID, movieID;
+    char input[64];
+    int loc, loc1;
+    while (fgets(buf, 256 * sizeof(char), fp) != NULL)
+    {
+        loc = 0;
+        input[0] = '\0'; // clear the array
+        // get userID
+        while (buf[loc] != ',')
+        {
+            input[loc] = buf[loc];
+            loc++;
+        }
+        input[loc++] = '\0';
+        userID = atoi(input);
+        // printf("UserID: %d\n", userID);
+
+        // get movieID
+        loc1 = 0;
+        input[0] = '\0';
+        while (buf[loc] != ',')
+        {
+            input[loc1++] = buf[loc];
+            loc++;
+        }
+        input[loc1] = '\0';
+        movieID = atoi(input);
+        // printf("movieID: %d\n", movieID);
+        users[userID] = appendMovies(users[userID], movieID);
+    }
+
+    fclose(fp);
+
+    fp = fopen("./movies.csv", 'r');
+
+    // 下标表示电影id
+    Genres *movies[NUM_MOVIES];
+
+
+    // TODO: 仿照我的代码填充*movies数组
+    // 李王子写 ok 你写吧
+    //
+
+    //
+    for(int i=0;i<NUM_MOVIES;i++)
+    {
+        movies[i]=NULL;
+    }
+
+
+    char*str=(char*)malloc(256*sizeof(char));
+
+    //读第一行
+    fgets(str, 256 * sizeof(char), fp); 
+    
+    //        fgets() returns s on success, and NULL on error or when end  of  file
+    //   occurs while no characters have been read.
+    //      你那个该写!=NULL 你看注释
+    //  ok 
+
+    
+    int id_index=0;
+
+    while(fgets(str,256*sizeof(char),fp)!=NULL)
+    {
+        
+
+    }
+
+
+
+    fclose(fp);
+
+    // 开始输出答案到文件answer.txt
+
+    fp = fopen("./answer.txt", 'w+'); // w+: 如果文件已存在先清空
+
+    int count[NUM_GENRES] = {};
+
+    // 开始从第一个用户循环 (1)
+    Movies *ptr;
+    for (int i = 1; i < NUM_GENRES; i++) {
+        cleararrInt(count, NUM_GENRES);
+        // 便历他喜欢的电影
+        ptr = users[i];
+        while (ptr != NULL) {
+            count[getGenreID(ptr->movieID, movies)] ++;
+            ptr = ptr->next;
+        }
+    }
+
+    //那个 就是你帮我写的那个数组 我感觉开个一维数组就可以了啊 
+
+    fclose(fp);
+
+    return 0;
+}
+
+Movies *appendMovies(Movies *last, int id)
+{
+    Movies *new = malloc(sizeof(Movies));
+
+    new->movieID = id;
+    new->next = NULL;
+
+    // 1.如果是null
+    if (last == NULL)
+    {
+        return new;
+    }
+    // 2.不是null，在最后加上新节点
+    Movies *ptr = last;
+
+    while (ptr->next != NULL)
+    {
+        ptr = ptr->next;
+    }
+
+    ptr->next = new;
+
+    return last;
+}
+
+
+int getGenreID(int movieID, Genres **movies) {
+    Genres *ptr = movies[movieID];
+}
+
+void clearArrInt(int* arr, int size) {
+    for (int i = 0; i < size; i++) {
+        arr[i] = 0;
+    }
+}
\ No newline at end of file
diff --git a/semester2/pset2/3-subLinkedList.c b/semester2/pset2/3-subLinkedList.c
new file mode 100644
index 0000000..d7ba740
--- /dev/null
+++ b/semester2/pset2/3-subLinkedList.c
@@ -0,0 +1,99 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct Node {
+	int data;
+	struct Node *next;
+} Node;
+
+Node *constructLinkedList();
+Node *appendLinkedList(Node *ptr, int data);
+void deleteLinkedList(Node *head);
+
+int main(void) {
+	Node *listA = constructLinkedList();
+	Node *listB = constructLinkedList();
+
+	Node *ptrA = listA, *ptrB, *ptrC;
+
+	int matched = 0;
+
+	while (ptrA != NULL) {
+		matched = 0;
+		ptrB = listB;
+
+		if (ptrA->data == ptrB->data) {
+			matched = 1;
+			ptrC = ptrA;
+
+			while (ptrB != NULL) {
+				if (ptrC == NULL) {
+					matched = 0;
+					break;
+				}
+				if (ptrC->data != ptrB->data) {
+					matched = 0;
+					break;
+				}
+				ptrB = ptrB->next;
+				ptrC = ptrC->next;
+
+			}
+
+		}
+
+		if (matched == 1) {
+			break;
+		}
+
+		ptrA = ptrA->next;
+	}
+
+	if (matched) {
+		printf("ListB is the sub sequence of ListA.");
+	} else {
+		printf("ListB is not the sub sequence of ListA.");
+	}
+
+	deleteLinkedList(listA);
+	deleteLinkedList(listB);
+	return 0;
+}
+
+Node *constructLinkedList() {
+	Node *head = malloc(sizeof(struct Node));
+	int buf;
+	scanf("%d", &buf);
+
+	head->data = buf;
+	head->next = NULL;
+	Node *ptr = head;
+	
+	scanf("%d", &buf);
+	while (buf != -1) {
+		ptr = appendLinkedList(ptr, buf);
+		scanf("%d", &buf);
+	}
+
+	return head;
+}
+
+Node *appendLinkedList(Node *ptr, int data) {
+	Node *new = malloc(sizeof(Node));
+
+	new->data = data;
+	new->next = NULL;
+
+	ptr->next = new;
+
+	return new;
+}
+
+void deleteLinkedList(Node *head) {
+	if (head == NULL) {
+		return;
+	} else {
+		deleteLinkedList(head->next);
+		free(head);
+	}
+}
diff --git a/semester2/pset2/4-splitNShift.c b/semester2/pset2/4-splitNShift.c
new file mode 100644
index 0000000..5608fc0
--- /dev/null
+++ b/semester2/pset2/4-splitNShift.c
@@ -0,0 +1,154 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct Node {
+  int data;
+  struct Node *next;
+} Node;
+
+Node *constructLinkedList();
+Node *appendLinkedList(Node *node, int data);
+void deleteLinkedList(Node *head);
+Node *segmentLinkedList(Node *head, Node **nextHead, int segLen);
+// returns the head of segmented Linked list, writes the head of next linked
+// list to *nextHead
+void connectLinkedList(Node *head1, Node *head2);
+// appends list2 to the end of list1
+void printLinkedList(Node *head);
+
+int main(void) {
+  Node *head = constructLinkedList();
+	/* printLinkedList(head); */
+
+  int s1, t1, s2, t2;
+  scanf("%d%d%d%d", &s1, &t1, &s2, &t2);
+
+  Node *tmp;
+  Node *ptr = head;
+  // start to iterate to s1
+  for (int i = 1; i < s1; i++) {
+    if (i == s1 - 1) {
+      tmp = ptr->next;
+      ptr->next = NULL;
+      ptr = tmp;
+    } else {
+      ptr = ptr->next;
+    }
+  }
+  Node *seg1, *seg2 = NULL, *seg3, *seg4 = NULL;
+  // get the first segment
+  seg1 = segmentLinkedList(ptr, &seg2, t1 - s1);
+	ptr = seg2;
+
+  for (int i = 0; i < s2 - t1 - 1; i++) {
+    if (i == s2 - t1 - 2) {
+      tmp = (Node*)(ptr->next);
+      ptr->next = NULL;
+      ptr = tmp;
+    } else {
+      ptr = ptr->next;
+    }
+  }
+  seg3 = segmentLinkedList(ptr, &seg4, t2 - s2);
+
+  // special cases:
+  // head == seg1
+  // seg2 == seg3
+  // seg4 == NULL
+
+	Node *newHead = head;
+
+  if (head != seg1) {
+    connectLinkedList(head, seg3);
+  } else {
+		newHead = seg3;
+	}
+  if (seg2 != seg3) {
+    connectLinkedList(seg3, seg2);
+  }
+  connectLinkedList(seg2, seg1);
+  if (seg4 != NULL) {
+    connectLinkedList(seg1, seg4);
+  }
+
+	printf("The new list is:");
+	printLinkedList(newHead);
+
+  deleteLinkedList(newHead);
+  return 0;
+}
+
+Node *constructLinkedList() {
+  int buf;
+  Node *head = malloc(sizeof(Node));
+  scanf("%d", &buf);
+  head->data = buf;
+  head->next = NULL;
+
+  Node *ptr = head;
+
+  scanf("%d", &buf);
+  while (buf != -1) {
+    ptr = appendLinkedList(ptr, buf);
+    scanf("%d", &buf);
+  }
+
+  return head;
+}
+
+Node *appendLinkedList(Node *node, int data) {
+  Node *new = malloc(sizeof(Node));
+
+  new->next = NULL;
+  new->data = data;
+
+  node->next = new;
+
+  return new;
+}
+
+void deleteLinkedList(Node *head) {
+  if (head == NULL) {
+    return;
+  } else {
+    deleteLinkedList(head->next);
+    free(head);
+  }
+}
+
+Node *segmentLinkedList(Node *head, Node **nextHead, int segLen) {
+  Node *ptr = head;
+  for (int i = 0; i < segLen; i++) {
+    ptr = ptr->next;
+  }
+
+  if (ptr->next != NULL) {
+    *nextHead = ptr->next;
+  }
+  ptr->next = NULL;
+
+  return head;
+}
+
+void connectLinkedList(Node *head1, Node *head2) {
+  Node *ptr = head1;
+
+  while (ptr->next != NULL) {
+    ptr = ptr->next;
+  }
+
+  ptr->next = head2;
+}
+
+void printLinkedList(Node *head) {
+	if (head != NULL)
+		printf("%d", head->data);
+
+	Node *ptr = head;
+	ptr = head->next;
+
+	while (ptr != NULL) {
+		printf(" %d", ptr->data);
+		ptr = ptr->next;
+	}
+}