zoukankan      html  css  js  c++  java
  • 双链表

    通过比较 index 和 size - index 的大小判断从头开始较快还是从尾巴开始较快

    public class ListNode {
      int val;
      ListNode next;
      ListNode prev;
      ListNode(int x) { val = x; } //这个只是用来初始化 隐藏的节点的
    }
    
    class MyLinkedList {
      int size;
      // sentinel nodes as pseudo-head and pseudo-tail
      ListNode head, tail;
      public MyLinkedList() {
        size = 0;
        head = new ListNode(0);
        tail = new ListNode(0);
        head.next = tail;
        tail.prev = head;
      }
    
      /** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */
      public int get(int index) {
        // if index is invalid
        if (index < 0 || index >= size) return -1;
    
        // choose the fastest way: to move from the head
        // or to move from the tail
        ListNode curr = head;
        if (index + 1 < size - index)
          for(int i = 0; i < index + 1; ++i) curr = curr.next;
        else {
          curr = tail;
          for(int i = 0; i < size - index; ++i) curr = curr.prev;
        }
    
        return curr.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. */
      public void addAtHead(int val) {
        ListNode pred = head, succ = head.next;
    
        ++size;
        ListNode toAdd = new ListNode(val);
        toAdd.prev = pred;
        toAdd.next = succ;
        pred.next = toAdd;
        succ.prev = toAdd;
      }
    
      /** Append a node of value val to the last element of the linked list. */
      public void addAtTail(int val) {
        ListNode succ = tail, pred = tail.prev;
    
        ++size;
        ListNode toAdd = new ListNode(val);
        toAdd.prev = pred;
        toAdd.next = succ;
        pred.next = toAdd;
        succ.prev = toAdd;
      }
    
      /** 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. */
      public void addAtIndex(int index, int val) {
        // If index is greater than the length, 
        // the node will not be inserted.
        if (index > size) return;
    
        // [so weird] If index is negative, 
        // the node will be inserted at the head of the list.
        if (index < 0) index = 0;
    
        // find predecessor and successor of the node to be added
        ListNode pred, succ;
        if (index < size - index) {
          pred = head;
          for(int i = 0; i < index; ++i) pred = pred.next;
          succ = pred.next;
        }
        else {
          succ = tail;
          for (int i = 0; i < size - index; ++i) succ = succ.prev;
          pred = succ.prev;
        }
    
        // insertion itself
        ++size;
        ListNode toAdd = new ListNode(val);
        toAdd.prev = pred;
        toAdd.next = succ;
        pred.next = toAdd;
        succ.prev = toAdd;
      }
    
      /** Delete the index-th node in the linked list, if the index is valid. */
      public void deleteAtIndex(int index) {
        // if the index is invalid, do nothing
        if (index < 0 || index >= size) return;
    
        // find predecessor and successor of the node to be deleted
        ListNode pred, succ;
        if (index < size - index) {
          pred = head;
          for(int i = 0; i < index; ++i) pred = pred.next;
          succ = pred.next.next;
        }
        else {
          succ = tail;
          for (int i = 0; i < size - index - 1; ++i) succ = succ.prev;
          pred = succ.prev.prev;
        }
    
        // delete pred.next 
        --size;
        pred.next = succ;
        succ.prev = pred;
      }
    }

     

  • 相关阅读:
    全排列
    RazorPages中的绑定
    SQL Server安装步骤
    2020-2021---开发工作总述
    C#.NET编程的特点
    VS自带Git的使用
    从apk反编译出.java文件
    基于页面的编程模型+关于设计的表达
    XtraReport注意事项
    Android总结
  • 原文地址:https://www.cnblogs.com/focusonoutput/p/13501468.html
Copyright © 2011-2022 走看看