From aa26a6eb1eb810581fb016db5edd92311c44ef5c Mon Sep 17 00:00:00 2001
From: NaiJi <naijiworld@protonmail.com>
Date: Fri, 26 Apr 2024 16:57:16 +0400
Subject: [PATCH] 7

---
 .../7. Linked List.c                          | 200 ++++++++++++++++++
 1 file changed, 200 insertions(+)
 create mode 100644 The Last Algorithms Course You'll Need/7. Linked List.c

diff --git a/The Last Algorithms Course You'll Need/7. Linked List.c b/The Last Algorithms Course You'll Need/7. Linked List.c
new file mode 100644
index 0000000..dd943e9
--- /dev/null
+++ b/The Last Algorithms Course You'll Need/7. Linked List.c	
@@ -0,0 +1,200 @@
+#include <stdio.h>
+#include "stdlib.h"
+
+typedef int BOOL;
+#define TRUE 1
+#define FALSE 0
+
+typedef struct node 
+{
+	int value;
+	struct node *next;
+	struct node *prev;
+} Node;
+
+typedef struct
+{
+	int value;
+	BOOL flag;
+} ListValue;
+
+static Node* HEAD;
+static Node* TAIL;
+
+static int LENGTH = 0;
+
+// O(1) operation, no growth by input
+BOOL append(int value)
+{
+	Node* new_head = malloc(sizeof(Node));
+	if (new_head == NULL)
+		return FALSE;
+
+	new_head->value = value;
+	new_head->prev = HEAD;
+
+	if (HEAD != NULL)
+		HEAD->next = new_head;
+	else
+		TAIL = new_head;
+
+	HEAD = new_head;
+	++LENGTH;
+
+	return TRUE;
+}
+
+// O(1) operation, no growth by input
+BOOL prepend(int value)
+{
+	Node* new_tail = malloc(sizeof(Node));
+	if (new_tail == NULL)
+		return FALSE;
+
+	new_tail->value = value;
+	new_tail->next = TAIL;
+
+	if (TAIL != NULL)
+		TAIL->prev = new_tail;
+	else
+		HEAD = new_tail;
+
+	TAIL = new_tail;
+	++LENGTH;
+
+	return TRUE;
+}
+
+// O(n) operation, the longer the list, the longer the search, by N in the worst case
+Node* get_node(int index)
+{
+	if (TAIL == NULL)
+		return NULL;
+
+	Node* iterator = TAIL;
+	while (index > 0 && iterator->next != NULL)
+	{
+		--index;
+		iterator = iterator->next;
+	}
+
+	if (index > 0)
+		return NULL;
+
+	return iterator;
+}
+
+// O(n) operation, the longer the list, the longer the search, by N in the worst case
+ListValue get(int index)
+{
+	ListValue result = { 0, FALSE };
+
+	Node* iterator = get_node(index);
+	if (iterator == NULL)
+		return result;
+
+	result.flag = TRUE;
+	result.value = iterator->value;
+
+	return result;
+}
+
+// O(n) operation, the longer the list, the longer the search, by N in the worst case
+BOOL insert_at(int index, int value)
+{
+	Node* iterator = get_node(index);
+	if (iterator == NULL)
+		return FALSE;
+
+	Node* new_node = malloc(sizeof(Node));
+	if (new_node == NULL)
+		return FALSE;
+
+	new_node->value = value;
+	new_node->next = iterator;
+
+	if (iterator->prev)
+	{
+		new_node->prev = iterator->prev;
+		iterator->prev->next = new_node;
+	}
+	else
+		TAIL = new_node;
+	
+	++LENGTH;
+	return TRUE;
+}
+
+// O(n) operation, the longer the list, the longer the search, by N in the worst case
+BOOL remove_at(int index)
+{
+	Node* iterator = get_node(index);
+	if (iterator == NULL)
+		return FALSE;
+
+	if (HEAD != TAIL)
+	{
+		if (iterator->next)
+			iterator->next->prev = iterator->prev;
+		else
+			HEAD = iterator->prev;
+
+		if (iterator->prev)
+			iterator->prev->next = iterator->next;
+		else
+			TAIL = iterator->next;
+	}
+	else
+	{
+		HEAD = NULL;
+		TAIL = NULL;
+	}
+
+	free(iterator);
+	iterator = NULL;
+
+	--LENGTH;
+	return TRUE;
+}
+
+int main()
+{
+	append(5);
+	append(22);
+	append(66);
+	prepend(122);
+	prepend(9);
+	insert_at(0, 999);
+	insert_at(3, 3);
+
+	Node* iterator = TAIL;
+	while (iterator != NULL)
+	{
+		printf("it: %d\n", iterator->value);
+		iterator = iterator->next;
+	}
+
+	printf("------\n");
+
+	remove_at(0);
+	remove_at(LENGTH-1);
+	printf("h: %d\n", HEAD->value);
+	printf("t: %d\n", TAIL->value);
+
+	iterator = TAIL;
+	while (iterator != NULL)
+	{
+		printf("it: %d\n", iterator->value);
+		iterator = iterator->next;
+	}
+
+	printf("------\n");
+
+	remove_at(1);
+	iterator = TAIL;
+	while (iterator != NULL)
+	{
+		printf("it: %d\n", iterator->value);
+		iterator = iterator->next;
+	}
+}