Merge pull request youngyangyang04#2639 from Relsola/master

Update 707.设计链表  优化 C 代码结构和逻辑

Author: youngyangyang04

problems/0707.设计链表.md

@@ -168,109 +168,103 @@ private:
 ### C:
 
 ```C
-typedef struct MyLinkedList {
-    int val;
-    struct MyLinkedList* next;
-}MyLinkedList;
+typedef struct Node {
+	int val;
+	struct Node* next;
+} Node;
+
+
+typedef struct {
+	int size;
+	Node* data;
+} MyLinkedList;
 
 /** Initialize your data structure here. */
 
 MyLinkedList* myLinkedListCreate() {
-    //这个题必须用虚拟头指针,参数都是一级指针,头节点确定后没法改指向了!!!
-    MyLinkedList* head = (MyLinkedList *)malloc(sizeof (MyLinkedList));
-    head->next = NULL;
-    return head;
+	MyLinkedList* obj = (MyLinkedList*)malloc(sizeof(MyLinkedList));
+    Node* head = (Node*)malloc(sizeof(Node));
+	head->next = (void*)0;
+	obj->data = head;
+    obj->size = 0;
+	return obj;
 }
 
 /** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */
 int myLinkedListGet(MyLinkedList* obj, int index) {
-    MyLinkedList *cur = obj->next;
-    for (int i = 0; cur != NULL; i++){
-        if (i == index){
-            return cur->val;
-        }
-        else{
-            cur = cur->next;
-        }
+	if (index < 0 || index >= obj->size) return -1;
+
+	Node* cur = obj->data;
+	while (index-- >= 0) {
+        cur = cur->next;
     }
-    return -1;
+
+	return cur->val;
 }
 
 /** Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list. */
 void myLinkedListAddAtHead(MyLinkedList* obj, int val) {
-    MyLinkedList *nhead = (MyLinkedList *)malloc(sizeof (MyLinkedList));
-    nhead->val = val;
-    nhead->next = obj->next;
-    obj->next = nhead;
+	Node* node = (Node*)malloc(sizeof(Node));
+	node->val = val;
 
+	node->next = obj->data->next;
+	obj->data->next = node;
+	obj->size++;
 }
 
 /** Append a node of value val to the last element of the linked list. */
 void myLinkedListAddAtTail(MyLinkedList* obj, int val) {
-    MyLinkedList *cur = obj;
-    while(cur->next != NULL){
+	Node* cur = obj->data;
+	while (cur->next != ((void*)0)) {
         cur = cur->next;
     }
-    MyLinkedList *ntail = (MyLinkedList *)malloc(sizeof (MyLinkedList));
-    ntail->val = val;
-    ntail->next = NULL;
-    cur->next = ntail;
+
+	Node* tail = (Node*)malloc(sizeof(Node));
+	tail->val = val;
+	tail->next = (void*)0;
+	cur->next = tail;
+	obj->size++;
 }
 
 /** Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted. */
 void myLinkedListAddAtIndex(MyLinkedList* obj, int index, int val) {
-    if (index == 0){
-        myLinkedListAddAtHead(obj, val);
-        return;
-    }
-    MyLinkedList *cur = obj->next;
-    for (int i = 1 ;cur != NULL; i++){
-        if (i == index){
-            MyLinkedList* newnode = (MyLinkedList *)malloc(sizeof (MyLinkedList));
-            newnode->val = val;
-            newnode->next = cur->next;
-            cur->next = newnode;
-            return;
-        }
-        else{
-            cur = cur->next;
-        }
+	if (index > obj->size) return;
+
+	Node* cur = obj->data;
+	while (index-- > 0) { 
+        cur = cur->next;
     }
+
+	Node* node = (Node*)malloc(sizeof(Node));
+	node->val = val;
+	node->next = cur->next;
+	cur->next = node;
+	obj->size++;
 }
 
 /** Delete the index-th node in the linked list, if the index is valid. */
 void myLinkedListDeleteAtIndex(MyLinkedList* obj, int index) {
-    if (index == 0){
-        MyLinkedList *tmp = obj->next;
-        if (tmp != NULL){
-            obj->next = tmp->next;
-            free(tmp);     
-        }
-        return;
-    }
-    MyLinkedList *cur = obj->next;
-    for (int i = 1 ;cur != NULL && cur->next != NULL; i++){
-        if (i == index){
-            MyLinkedList *tmp = cur->next;
-            if (tmp != NULL) {
-                cur->next = tmp->next;
-                free(tmp);
-            }
-            return;
-        }
-        else{
-            cur = cur->next;
-        }
+	if (index < 0 || index >= obj->size) return;
+
+	Node* cur = obj->data;
+	while (index-- > 0) {
+        cur = cur->next;
     }
-    
+
+	Node* temp = cur->next;
+	cur->next = temp->next;
+	free(temp);
+	obj->size--;
 }
 
 void myLinkedListFree(MyLinkedList* obj) {
-    while(obj != NULL){
-        MyLinkedList *tmp = obj;
-        obj = obj->next;
-        free(tmp);
-    }
+	Node* tmp = obj->data;
+	while (tmp != NULL) {
+		Node* n = tmp;
+		tmp = tmp->next;
+		free(n);
+	}
+	free(obj);
 }
 
 /**
@@ -1569,3 +1563,4 @@ public class MyLinkedList
 <a href="https://programmercarl.com/other/kstar.html" target="_blank">
   <img src="../pics/网站星球宣传海报.jpg" width="1000"/>
 </a>
+