Cracking the coding interview--Q2.2

Implement an algorithm to find the kth to last element of a singly linked list.

实现一个算法寻找链表中倒数第K个数..

 

解答：

关于链表的问题，书中也提到了关键的两个技巧，一个是递归；另一个是 The"Runner"Technique，也就是使用两个指针同时遍历链表的方式。这道题可以分别用这两种方法来解决。

import java.util.HashMap;



public class List {

    int data;

    List next;



    public List(int d) {

        this.data = d;

        this.next = null;

    }



    public void appendToTail(int d) {

        List end = new List(d);

        List n = this;

        while (n.next != null) {

            n = n.next;

        }

        n.next = end;

    }



    public void print() {

        List n = this;

        System.out.print("{");

        while (n != null) {

            if (n.next != null)

                System.out.print(n.data + ", ");

            else

                System.out.println(n.data + "}");

            n = n.next;

        }

    }



    public int nthToLast(int n) {

        if (this.next == null) {

            if (n == 0)

                System.out.println(this.data);

            return 0;

        }

        int i = this.next.nthToLast(n) + 1;

        if (i == n)

            System.out.println(this.data);

        return i;

    }



    public void nthToLast1(int n) {

        List m = this;

        List pt = this;

        for (int i = 0; i < n; i++){

            if(pt.next == null)

                return ;

            pt = pt.next;

        }

        while(pt.next != null)

        {

            m = m.next;

            pt = pt.next;

        }

        System.out.println(m.data);

    }



    public static void main(String args[]) {

        List list = new List(0);

        list.appendToTail(1);

        list.appendToTail(2);

        list.appendToTail(3);

        list.appendToTail(4);

        list.appendToTail(5);

        list.appendToTail(6);

        list.appendToTail(7);

        list.appendToTail(8);

        list.appendToTail(9);

        list.print();

        list.nthToLast(10);

        list.nthToLast1(10);

    }

}