From 9891f38ddcca971fa21ab61e7a70832c8c877b0a Mon Sep 17 00:00:00 2001
From: Michael Hunteman <michael@huntm.net>
Date: Sat, 23 Sep 2023 12:53:46 -0500
Subject: Initial commit

---
 doublylinkedlist.c | 161 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 161 insertions(+)
 create mode 100644 doublylinkedlist.c

(limited to 'doublylinkedlist.c')

diff --git a/doublylinkedlist.c b/doublylinkedlist.c
new file mode 100644
index 0000000..e98217a
--- /dev/null
+++ b/doublylinkedlist.c
@@ -0,0 +1,161 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+struct node {
+	int val;
+	struct node *prev;
+	struct node *next;
+};
+
+struct node *head;
+struct node *tail;
+int len = 0;
+
+void
+prepend(int val)
+{
+	struct node *tmp = malloc(sizeof(struct node));
+	tmp->val = val;
+	if (head == NULL) {
+		head = tail = tmp;
+		return;
+	}
+	tmp->val = val;
+	tmp->next = head;
+	head->prev = tmp;
+	head = tmp;
+	++len;
+}
+
+void
+append(int val)
+{
+	struct node *tmp = malloc(sizeof(struct node));
+	tmp->val = val;
+	if (!tail) {
+		head = tail = tmp;
+		return;
+	}
+	tmp->prev = tail;
+	tail->next = tmp;
+	tail = tmp;
+	++len;
+}
+
+struct node
+*get_at(int i)
+{
+	struct node *cur = head;
+	for (int j = 0; cur && j < i; ++j) {
+		cur = cur->next;
+	}
+	return cur;
+}
+
+void
+insert_at(int val, int i)
+{
+	if (i > len) {
+		printf("index is greater than the list length\n");
+	} else if (i == len) {
+		append(val);
+		return;
+	} else if (i == 0) {
+		prepend(val);
+		return;
+	}
+	struct node *cur = get_at(i);
+	struct node *tmp = malloc(sizeof(struct node));
+	tmp->next = cur;
+	tmp->prev = cur->prev;
+	cur->prev = tmp;
+
+	if (tmp->prev) {
+		tmp->prev->next = tmp;
+	}
+	++len;
+}
+
+int
+remove_node(struct node *tmp)
+{
+	--len;
+	if (len == 0) {
+		head = tail = NULL;
+		return -1;
+	}
+
+	if (tmp->prev) {
+		tmp->prev->next = tmp->next;
+	}
+	if (tmp->next) {
+		tmp->next->prev = tmp->prev;
+	}
+
+	if (tmp == head) {
+		head = tmp->next;
+	}
+	if (tmp == tail) {
+		tail = tmp->prev;
+	}
+
+	int val = tmp->val;
+	free(tmp);
+	return val;
+}
+
+int
+remove_val(int val)
+{
+	struct node *cur = head;
+	for (int i = 0; cur && cur->val != val && i < len; ++i) {
+		cur = cur->next;
+	}
+	if (!cur) {
+		return -1;
+	}
+	return remove_node(cur);
+}
+
+int
+remove_at(int i)
+{
+	struct node *tmp = get_at(i);
+	if (!tmp) {
+		return -1;
+	}
+	return remove_node(tmp);
+}
+
+int
+get(int i)
+{
+	get_at(i)->val;
+}
+
+void
+print()
+{
+	struct node *cur = head;
+	while (cur != NULL) {
+		printf("%d ", cur->val);
+		cur = cur->next;
+	}
+	printf("\n");
+}
+
+int
+main()
+{
+	int val, n = 0;
+	printf("How many integers?\n");
+	scanf("%d", &n);
+	for (int i = 0; i < n; ++i) {
+		printf("Enter an integer \n");
+		scanf("%d", &val);
+		prepend(val);
+		print();
+	}
+
+	return 0;
+}
-- 
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