递归

Author: tianqing.liang

05LinkedList/LinkedList.dart

@@ -3,7 +3,7 @@ class LinkedList<T> {
   late int _size;
 
   LinkedList() {
-    _dummyHead = new _Node.all(null,null);
+    _dummyHead = new _Node.withEmpty();
     _size = 0;
   }
 
@@ -52,7 +52,7 @@ class LinkedList<T> {
     for (var i = 0; i < index; i++) {
       prev = prev?.next;
     }
-    _Node _node = new _Node.head(t);
+    _Node _node = new _Node.wihtHead(t);
     _node.next = prev?.next;
     prev?.next = _node;
     _size++;
@@ -127,12 +127,12 @@ class _Node<T> {
 
   T? t;
 
-  _Node.empty();
+  _Node.withEmpty();
 
-  _Node.all(this.t, this.next);
+  _Node.withAll(this.t, this.next);
 
-  factory _Node.head(T t) {
-    var result = new _Node.all(t,  null);
+  factory _Node.wihtHead(T t) {
+    var result = new _Node.withAll(t,  null);
     return result;
   }
 

05LinkedList/LinkedListQueue.dart

@@ -1,32 +1,75 @@
 import 'Queue.dart';
+
+/**
+ * 带尾结点的队列
+ */
 class LinkedListQueue implements Queue{
+
+  late _Node? _head;
+  late _Node? _tail;
+  late int _size;
+
+  LinkedListQueue(){
+    _head = null;
+    _tail = null;
+    _size = 0;
+  }
+
   @override
   dequeue() {
-    // TODO: implement dequeue
-    throw UnimplementedError();
+    if (isEmpty()) {
+      throw Exception("Cannot dequeue from an empty queue");
+    }
+    _Node retNode = _head!;
+    _head = _head!.next;
+    retNode.next = null;
+    if(_head == null){
+      _tail =null;
+    }
+    _size --;
+    return retNode.t;
   }
 
   @override
   void enqueue(e) {
-    // TODO: implement enqueue
+    if(_tail == null){
+      _tail = _Node.wihtHead(e);
+      _head = _tail;
+    }else{
+    _tail!.next =_Node.wihtHead(e);
+    _tail = _tail!.next;
+    }
+    _size++;
   }
 
   @override
   getFront() {
-    // TODO: implement getFront
-    throw UnimplementedError();
+    if (isEmpty()) {
+      throw Exception("Queue is empty");
+    }
+    return _head!.t;
   }
 
   @override
   int getSize() {
-    // TODO: implement getSize
-    throw UnimplementedError();
+    return _size;
   }
 
   @override
   bool isEmpty() {
-    // TODO: implement isEmpty
-    throw UnimplementedError();
+    return _size == 0;
+  }
+
+  @override
+  String toString() {
+    StringBuffer res =new StringBuffer();
+    res.write("Queue: front ");
+    for(_Node? cur = _head!.next ; cur != null ; cur = cur.next){
+      res.write(cur);
+      res.write("->");
+    }
+    res.write("NULL tail");
+    return res.toString();
   }
 
 }
@@ -37,17 +80,29 @@ class _Node<T> {
 
   T? t;
 
-  _Node.empty();
+  _Node();
 
-  _Node.all(this.t, this.next);
+  _Node.withAll(this.t, this.next);
 
-  factory _Node.head(T t) {
-    var result = new _Node.all(t,  null);
+  factory _Node.wihtHead(T t) {
+    var result = new _Node.withAll(t,  null);
     return result;
   }
 
   @override
   String toString() {
     return t.toString();
   }
+}
+
+void main(){
+  LinkedListQueue queue = new LinkedListQueue();
+  for(int i = 0 ; i < 10 ; i ++){
+    queue.enqueue(i);
+    print(queue);
+    if(i % 3 ==2){
+      queue.dequeue();
+      print(queue);
+    }
+  }
 }

05LinkedList/main.dart

@@ -1,5 +1,6 @@
 import 'LinkedList.dart';
 import 'LinkedListStatck.dart';
+import 'LinkedListQueue.dart';
 void main(){
   LinkedList linkedList = new LinkedList();
   for(int i = 0 ; i < 5 ; i ++){
@@ -20,4 +21,12 @@ void main(){
     stack.push(i);
     print(stack);
   }
+  LinkedListQueue queue = new LinkedListQueue();
+  for(int i = 0 ; i < 10 ; i ++){
+    queue.enqueue(i);
+    if(i % 3 ==2){
+      queue.dequeue();
+      print(queue);
+    }
+  }
 }

06Recursion/ListNode.dart

@@ -0,0 +1,36 @@
+class ListNode{
+
+  int? val;
+  ListNode? next;
+
+  ListNode(this.val);
+
+  ListNode.withArray(List arr){
+    if(arr == null || arr.length == 0){
+      throw Exception("arr cannot be empty");
+    }
+    this.val = arr[0];
+    ListNode cur = this;
+    for(var i = 1;i<arr.length;i++){
+      cur.next = ListNode(arr[i]);
+      cur = cur.next!;
+    }
+  }
+  @override
+  String toString() {
+    StringBuffer s = new StringBuffer();
+    ListNode cur =this;
+    while(cur !=null){
+      s.write("${cur.val} ->");
+      if(cur.next !=null){
+        cur = cur.next!;
+      }else{
+        break;
+      }
+    }
+    s.write("NULL");
+    return s.toString();
+  }
+
+
+}

06Recursion/Solution3.dart

@@ -0,0 +1,38 @@
+import 'ListNode.dart';
+class Solution3{
+
+  static ListNode? removeElements(ListNode head,int val){
+    ListNode dummyHead = new ListNode(-1);
+    dummyHead.next = head;
+
+    ListNode prev = dummyHead;
+    while(prev.next!=null){
+      if(prev.next!.val == val){
+        prev.next = prev.next!.next;
+      }else{
+        prev = prev.next!;
+      }
+    }
+    return dummyHead.next;
+    if(head == null){
+      return head;
+    }
+//    ListNode? res = removeElements(head.next!, val);
+//    if(head.val == val){
+//      return res;
+//    }else{
+//      head.next = res;
+//      return head;
+//    };
+
+  }
+}
+void main(){
+  var nums = [1,2,6,3,4,5,6];
+  ListNode listNode =ListNode.withArray(nums);
+  print(listNode);
+  
+  ListNode? res = Solution3.removeElements(listNode, 6);
+  print(res);
+
+}

06Recursion/Sum.dart

@@ -0,0 +1,21 @@
+/**
+ * 递归
+ */
+class Sum{
+
+  static int sum(List arr){
+    return sumRecurison(arr,0);
+  }
+  static int sumRecurison(List arr,int l){
+    if(l == arr.length){
+      return 0;
+    }
+      return arr[l]+sumRecurison(arr,l+1);
+  }
+}
+
+void  main(){
+  List nums = [1,2,3,4,5,6,7,8];
+  int result = Sum.sum(nums);
+  print("结果：$result");
+}

README.md

@@ -6,5 +6,6 @@
 2. 选择排序
 3. 插入排序
 4. 栈，队列，循环队列
-5. 链表，链表实现栈
+5. 链表，链表实现栈，链表实现队列
+6. 递归