From e07bb4eee0330057b9254bc8deab7611ca471bc3 Mon Sep 17 00:00:00 2001
From: jacekpoz <jacekpoz@cock.li>
Date: Mon, 11 Mar 2024 12:01:09 +0100
Subject: [PATCH] improve linked list insert and merge from O(n) to O(1)

just keeping track of the tail is enough to do that
---
 lab01/zad2/include/linked_list.h |  1 +
 lab01/zad2/src/linked_list.c     | 27 +++++++--------------------
 2 files changed, 8 insertions(+), 20 deletions(-)

diff --git a/lab01/zad2/include/linked_list.h b/lab01/zad2/include/linked_list.h
index 54e3a1b..0531aab 100644
--- a/lab01/zad2/include/linked_list.h
+++ b/lab01/zad2/include/linked_list.h
@@ -13,6 +13,7 @@ typedef struct {
     size_t length;
     size_t element_size;
     Node *head;
+    Node *tail;
 } LinkedList;
 
 typedef struct {
diff --git a/lab01/zad2/src/linked_list.c b/lab01/zad2/src/linked_list.c
index 755fe31..317004e 100644
--- a/lab01/zad2/src/linked_list.c
+++ b/lab01/zad2/src/linked_list.c
@@ -16,6 +16,7 @@ LinkedList linked_list_new(size_t element_size) {
     ret.length = 0;
     ret.element_size = element_size;
     ret.head = NULL;
+    ret.tail = NULL;
 
     return ret;
 }
@@ -24,17 +25,14 @@ void linked_list_insert(LinkedList *l, void *value) {
     if (l->head == NULL) {
         l->head = node_new(value, l->element_size);
         l->head->next = l->head;
+        l->tail = l->head;
         l->length += 1;
         return;
     }
 
-    Node *tail = l->head;
-    while (tail->next != l->head) {
-        tail = tail->next;
-    }
-
-    tail->next = node_new(value, l->element_size);
-    tail->next->next = l->head;
+    l->tail->next = node_new(value, l->element_size);
+    l->tail->next->next = l->head;
+    l->tail = l->tail->next;
     l->length += 1;
 }
 
@@ -42,19 +40,8 @@ LinkedList linked_list_merge(LinkedList l1, LinkedList l2) {
     if (l1.head == NULL) return l2;
     if (l2.head == NULL) return l1;
 
-    Node *l1_tail = l1.head;
-    while (l1_tail->next != l1.head) {
-        l1_tail = l1_tail->next;
-    }
-
-    l1_tail->next = l2.head;
-
-    Node *l2_tail = l2.head;
-    while (l2_tail->next != l2.head) {
-        l2_tail = l2_tail->next;
-    }
-
-    l2_tail->next = l1.head;
+    l1.tail->next = l2.head;
+    l2.tail->next = l1.head;
 
     l1.length += l2.length;