大杂烩 -- 查找单向链表倒数第m个元素

基础大杂烩 -- 目录

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1.输入并查找

　　方案：头插法，正向查找第m个元素。

import java.util.Scanner;
 
public class Main {
 
    /**
     * @param args
     */
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNext()) {
            ListNode node = new ListNode();
            node.next = null;
            int N = in.nextInt();
             
            for (int i = 0; i < N; i++) {
                ListNode p = new ListNode();
                int x = in.nextInt();
                p.next = node.next;
                p.data = x;
                node.next = p;
            }
            int k = in.nextInt();
            ListNode kthNode = getKthNode(node,k);
            System.out.println(kthNode.data);
        }
    }
     
    public static ListNode getKthNode(ListNode node,int k){
        ListNode front = node,behind = node;
        int x=0;
        while(front.next!=null && x<=k){
            x++;
            front = front.next;
        }
        return front;
    }
}
 
class ListNode {
    public int data;
    public ListNode next;
}

2.指定单向链表并查找倒数第m个元素

　　两种情况：无环、有环

　　　　无环方案：因为无环单向链表最后一个元素next一定为null，因此设置两个指针slow = head ，fast = head + m，当fast.next == null时slow.next恰好是倒数第m个元素。

　　　　有环方案：查找连接点，分割成无环单向链表，最后一个元素next一定为连接点join，将最后一个元素next --> null，此时用无环方案即可解决。因此设置连个指针slow = head ，fast = head + m，当fast.next == null时slow.next恰好是倒数第m个元素。

　　无环方案Class ： 

package limeMianShi.link;

public class Test01 {

    public static void main(String[] args) {
        ListNode head = new ListNode(0);
        ListNode p = head;
        for (int i = 1; i <= 10; i++) {
            ListNode node = new ListNode(i);
            p.next = node;
            p = node;

        }
        printListNode(head);
        printKElement(head,3);
    }

    private static void printKElement(ListNode head, int m) {
        if(m == 0){
            System.out.println("null");
        }
        ListNode p = head;
        if(m > 0){
            for(int i = 0;i < m;i++){
                if(i == m - 1){
                    System.out.println("正数第" + m + "个元素为： " + p.data);
                }
                p = p.next;
            }
        }else{
            ListNode s = head;
            for(int i = 0;i < -m;i++){
                p = p.next;
            }
            while(null != p){
                s = s.next;
                p = p.next;
            }
            System.out.println("倒数第" + (-m) + "个元素为： " + s.data);
        }
    }

    private static void printListNode(ListNode head) {
        if (null != head) {
            System.out.print(head.data + " --> ");
            printListNode(head.next);
        }else{
            System.out.println("null");
        }
    }
}

class ListNode {

    public int data;
    public ListNode next;

    public ListNode() {
        super();
    }

    public ListNode(int data) {
        this.data = data;
    }
}

　　有环方案Class ： 

package limeMianShi.link;

public class Test02 {

    public static void main(String[] args) {
        ListNode head = new ListNode(0);
        ListNode p = head;
        ListNode p4 = null;
        for (int i = 1; i <= 10; i++) {
            ListNode node = new ListNode(i);
            p.next = node;
            p = node;
            if (i == 4) {
                p4 = node;
            }
        }
        p.next = p4;
        pullLoop(head);
        printListNode(head);
        for (int i = 1; i < 11; i++) {
            printKElement(head, -i);
        }
    }

    private static void printListNode(ListNode head) {
        if (null != head) {
            System.out.print(head.data + " --> ");
            printListNode(head.next);
        } else {
            System.out.println("null");
        }
    }

    private static void printKElement(ListNode head, int m) {
        if (m == 0) {
            System.out.println("null");
        }
        ListNode p = head;
        if (m > 0) {
            for (int i = 0; i < m; i++) {
                if (i == m - 1) {
                    System.out.println("正数第" + m + "个元素为： " + p.data);
                }
                p = p.next;
            }
        } else {
            ListNode s = head;
            for (int i = 0; i < -m; i++) {
                p = p.next;
            }
            while (null != p) {
                s = s.next;
                p = p.next;
            }
            System.out.println("倒数第" + (-m) + "个元素为： " + s.data);
        }
    }

    private static void pullLoop(ListNode head) {
        ListNode p = getP(head);
        ListNode pre = null;
        while (head != p) {
            pre = p;
            head = head.next;
            p = p.next;
        }
        pre.next = null;
    }

    private static ListNode getP(ListNode head) {
        ListNode solw = head.next;
        ListNode fast = head.next.next;
        while (solw != fast) {
            solw = solw.next;
            fast = fast.next.next;
        }
        return solw;
    }
}

class ListNode {
    public int data;
    public ListNode next;

    public ListNode() {
    }

    public ListNode(int data) {
        this.data = data;
    }
}

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