数据结构之链表

package com.dby.link;

/** * Created by suzunshou on 2016/4/11. * 链表的元素不能随机访问 * 元素前面和后面不会出现多个元素相连的情况 * 元素相互依赖，串联而成 * 链表只有一个表头 */
public class LinkedList {
    //结点类
    private class Node {
        //数据
        private Object data;
        //下一个结点的地址
        private Node next = null;

        public Node(Object data) {
            this.data = data;
        }

    }

    private Node first = null;
    private Node last = null;
    private int size;

    //在首部插入结点
    public void insertFirst(Object data) {
        //创建一个新结点
        Node newNode = new Node(data);
        //结点指向原来的first结点
        newNode.next = first;
        //将结点赋值给first结点
        first = newNode;
        Node p = first;
        Node q = null;
        //遍历查找最后一个结点
        while (p != null) {
            q = p;
            p = p.next;
        }
        //将结点放到尾结点
        last = q;
        size++;
    }

    //链表尾部插入结点
    public void insertLast(Object data) {
        //新结点
        Node newNode = new Node(data);
        //空链表的话，新结点放first
        if (first == null) {
            first = newNode;
        } else {
            Node p = first;
            Node q = null;
            //遍历查找最后一个结点
            while (p != null) {
                q = p;
                p = p.next;
            }
            //将结点放到尾结点
            q.next = newNode;
            last = newNode;
        }
        size++;
    }

    //插入结点到某个位置
    public void insert(Object data, int index) {
        //新结点
        Node newNode = new Node(data);
        //空链表
        if (first == null) {
            first = newNode;
            return;
        }
        //只有一个结点
        if (index - 1 == 0) {
            newNode.next = first;
            first = newNode;
            return;
        }
        //普通情况
        Node curr = first;
        int count = 0;
        //遍历找到索引处的结点
        while (curr.next != null && count < index - 2) {
            curr = curr.next;
            count++;
        }
        //插入结点，把前一个结点和后一个结点断开，两端接上新结点
        if (count == index - 2) {
            newNode.next = curr.next;
            curr.next = newNode;
        }
    }

    //查找所有结点
    public void findAll() {
        //空结点
        if (first == null)
            return;
        //遍历结点
        Node cur = first;
        while (cur != null) {
            System.out.print(cur.data + "->");
            cur = cur.next;
        }
        System.out.println("\n");
    }

    //反转链表
    public void reverse() {
        //空链表
        if (first == null) {
            return;
        }
        Node next_node, curr_node;
        //第二个结点
        curr_node = first.next;
        //断开第一第二个结点
        first.next = null;
        //反转相当于每次都findOne+insertFirst
        while (curr_node != null) {
            //第三个结点
            next_node = curr_node.next;

            //把第一个结点接到第二个结点的另一端
            curr_node.next = first;
            //把第二个结点变成新的第一个结点
            first = curr_node;

            //移动到下一个结点
            curr_node = next_node;
        }
    }

    //删除首结点
    public void deleteFirst() {
        //空结点
        if (first == null)
            return;
        //指针移向first结点指向的结点的下一个结点
        first = first.next;
        size--;
    }

    //删除尾结点
    public void deleteLast() {
        //空链表
        if (first == null)
            return;
        //只有一个结点
        if (first.next == null) {
            first = null;
            size--;
        } else {
            //多个结点
            Node p = first;
            Node q = null;
            //遍历结点，找出倒数第2个结点
            while (p.next != null) {
                q = p;
                p = p.next;
            }
            //删除最后一个结点
            q.next = null;
            size--;
        }

    }

    //根据数据查找结点
    public Node findOne(Object data) {
        //空链表
        if (first == null)
            return null;
        //令当前结点为first结点
        Node cur = first;
        //遍历结点
        while (cur != null) {
            //查找到了，返回
            if (cur.data.equals(data)) {
                return cur;
            } else {
                //否则，继续查找下一个结点
                cur = cur.next;
            }
        }
        return null;
    }

    //根据索引找出结点
    public Node findByIndex(int index) {
        if (index - 1 > size) {

        } else {
            Node curr = first;
            for (int i = 1; i < index; i++) {
                curr = curr.next;
            }
            return curr;
        }
        return null;
    }

    //是否为空
    public boolean isEmpty() {
        return (size == 0);
    }


    //删除某一个结点
    public void remove(Object data) {
        //空链表
        if (first == null) {
            return;
        }
        //单结点链表
        if (first.data.equals(data)) {
            first = first.next;
            size--;
        } else {
            //前一个结点
            Node prev = first;
            //中间结点
            Node cur = first.next;
            while (cur != null) {
                if (cur.data.equals(data)) {
                    //后一个结点接到前一个结点，顶替中间结点
                    prev.next = cur.next;
                    size--;
                }
                //否则，前一个结点移动到下一个结点
                prev = cur;
                //中间结点移动到下一个结点
                cur = cur.next;
            }

        }
    }

    //根据索引删除结点
    public void removeByIndex(int index) {
        //空链表
        if (first == null) {
            return;
        }
        //单结点
        Node curr = first;
        int count = 0;
        if (index - 1 == 0) {
            first = first.next;
            return;
        }
        //普通情况，找到结点
        while (curr.next != null && count < index - 2) {
            curr = curr.next;
            count++;
        }
        //删除结点
        if (count == index - 2 && curr.next != null) {
            Node delete_node = curr.next;
            curr.next = delete_node.next;
            delete_node = null;
        }
        size--;
    }

    public static void main(String[] args) {
        LinkedList ll = new LinkedList();
        for (int i = 1; i < 8; i++) {
            ll.insertLast(i);
        }
        ll.removeByIndex(2);
        ll.removeByIndex(4);
        ll.findAll();
        System.out.println(ll.findByIndex((ll.size + 1) / 2).data);
        ll.insert(2,2);
        ll.insertFirst(0);
        System.out.println(ll.findOne(2).data);
        ll.findAll();
    }
}