Stack<ListNode> stack = new Stack<>();
时间: 2023-11-17 09:06:53 浏览: 141
This line of code creates a new instance of a generic Stack class with a parameterized type of ListNode. The Stack class is a collection that implements the last-in-first-out (LIFO) data structure, meaning that the last element added to the stack will be the first one to be removed.
In this case, the stack will contain ListNode objects, which are typically used to represent nodes in a linked list data structure. This Stack object can be used to implement various algorithms, such as a depth-first search or a reverse traversal of a linked list.
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import java.util.Stack; public class Solution { public ListNode ReverseList(ListNode head) { Stack<ListNode> stack= new Stack<>(); //把链表节点全部摘掉放到栈中 while (head != null) { stack.push(head); head = head.next; } if (stack.isEmpty()) return null; ListNode node = stack.pop(); ListNode dummy = node; //栈中的结点全部出栈,然后重新连成一个新的链表 while (!stack.isEmpty()) { ListNode tempNode = stack.pop(); node.next = tempNode; node = node.next; } //最后一个结点就是反转前的头结点,一定要让他的next //等于空,否则会构成环 node.next = null; return dummy; } }
这段代码是一个用于反转链表的方法。让我来解释一下代码的逻辑:
首先,代码创建了一个名为 `stack` 的栈,用于存储链表节点。
```java
Stack<ListNode> stack = new Stack<>();
```
接下来,代码使用一个循环遍历链表,并将每个节点压入栈中。
```java
while (head != null) {
stack.push(head);
head = head.next;
}
```
然后,代码检查栈是否为空。如果栈为空,说明链表中没有节点,那么返回 `null`。
```java
if (stack.isEmpty())
return null;
```
接着,代码从栈中弹出一个节点,并将它赋值给 `node` 变量。
```java
ListNode node = stack.pop();
```
然后,代码将 `node` 赋值给 `dummy` 变量。
```java
ListNode dummy = node;
```
接下来,代码使用另一个循环从栈中弹出节点,并将它们重新连接成一个新的链表。
```java
while (!stack.isEmpty()) {
ListNode tempNode = stack.pop();
node.next = tempNode;
node = node.next;
}
```
最后,代码将最后一个节点的 `next` 设置为 `null`,以避免形成循环,并返回反转后的链表的头节点 `dummy`。
```java
node.next = null;
return dummy;
```
这段代码的作用是将原始链表逆序,并返回逆序后的新链表的头节点。
ListNode node = stack.pop(); ListNode dummy = node;
This code snippet pops the top element from a stack of ListNode objects and assigns it to the variable "node". Then, it creates a new ListNode object called "dummy" and assigns it the same value as "node". This can be useful in situations where you need to manipulate the original node but also want to keep a reference to the original value for later use.