New semester!

semester2/pset1/1-linkedList.c

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+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct Node {
+  int data;
+  struct Node *next;
+} Node;
+
+Node *appendNode(Node *n) {
+  int data;
+  scanf("%d", &data);
+  Node *node = malloc(sizeof(struct Node));
+  node->data = data;
+  node->next = NULL;
+  n->next = node;
+  return node;
+}
+
+Node *makeList(int col) {
+  Node *head, *ptr;
+  head = malloc(sizeof(Node));
+  head->next = NULL;
+
+  ptr = head;
+  for (int i = 0; i < col; i++) {
+    ptr = appendNode(ptr);
+  }
+  return head;
+}
+
+void delete(Node *head) {
+	if (head->next == NULL) {
+		free(head);
+	} else {
+		delete(head->next);
+	}
+}
+
+int main(void) {
+  int rows;
+  int col;
+  int count;
+  scanf("%d", &rows);
+  Node *ptr;
+
+  for (int i = 0; i < rows; i++) {
+    scanf("%d", &col);
+    Node *head = makeList(col);
+
+    count = 0;
+    for (ptr = head->next; ptr != NULL; ptr = ptr->next) {
+      if (count % 2 == 1) {
+        if (count == 1) {
+          printf("%d", ptr->data);
+        } else {
+          printf(" %d", ptr->data);
+        }
+      }
+      count++;
+    }
+    printf("\n");
+
+		delete(head);
+  }
+
+  return 0;
+}

semester2/pset1/2-reverseLinkedList.c

@@ -0,0 +1,96 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct Node {
+  struct Node *next;
+  struct Node *prev;
+  int data;
+} Node;
+
+// Returns the head of the linked list
+Node *newLinkedList();
+// Returns a pointer to the next node
+Node *appendNode(Node *prev);
+// Prints the linked list in reverse order
+void printListReverse(Node *head);
+// Frees the list from memory
+void freeList(Node *head);
+
+int main(void) {
+  // Get rows of input
+  int rows;
+  scanf("%d", &rows);
+
+  Node *head;
+  for (int i = 0; i < rows; i++) {
+    head = newLinkedList();
+    printListReverse(head);
+    freeList(head);
+  }
+
+  return 0;
+}
+
+Node *newLinkedList() {
+  Node *ptr, *head;
+
+  // Initialize head
+  head = malloc(sizeof(Node));
+  head->prev = NULL;
+  head->next = NULL;
+
+  ptr = head;
+
+  // Initialize list
+  int data;
+  scanf("%d", &data);
+  while (data != -1) {
+    ptr->data = data;
+    ptr = appendNode(ptr);
+    scanf("%d", &data);
+  }
+
+  return head;
+}
+
+Node *appendNode(Node *prev) {
+  Node *node;
+  node = malloc(sizeof(Node));
+
+  prev->next = node;
+
+  node->prev = prev;
+  node->next = NULL;
+
+  return node;
+}
+
+void printListReverse(Node *head) {
+  // Can't use recursion because the output should be formatted
+  Node *ptr = head;
+  while (ptr->next != NULL) {
+    ptr = ptr->next;
+  }
+  // ptr now points to the tail.
+
+	ptr = ptr->prev;
+	if (ptr != NULL) {
+		printf("%d", ptr->data);
+		ptr = ptr->prev;
+	}
+  while (ptr != NULL) {
+    printf(" %d", ptr->data);
+    ptr = ptr->prev;
+  }
+
+  printf("\n");
+}
+
+void freeList(Node *head) {
+  if (head->next != NULL) {
+    freeList(head->next);
+    free(head);
+  } else {
+    free(head);
+  }
+}

semester2/pset1/README.md

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+# Pset 1
+
+## Info
+
+the problem set can be found [here](https://pintia.cn/problem-sets/1499923457155141632)