Cracking the coding interview--Q2.4

Write code to partition a linked list around a value x, such that all nodes less than x
come before alt nodes greater than or equal to.

分割一个链表，将值小于x的节点全部放在其他节点的前面。

解答：

我们可以创建两个不同的链表，其中一个用来连接比x小的节点，另外一个则连接大于等于x的节点，然后合并两个链表即可。

public class Main {

    public static void appendToTail(List head, int d) {

        List end = new List(d);

        List n = head;

        while (n.next != null) {

            n = n.next;

        }

        n.next = end;

    }



    public static void print(List head) {

        List n = head;

        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 static List partition(List head, int x) {

        List small = null;

        List large = null;

        List largeHead = null;

        List smallHead = null;

        while (head != null) {

            List next = head.next;

            head.next = null;

            if (head.data < x) {

                if (small == null) {

                    small = head;

                    smallHead = small;

                } else {

                    small.next = head;

                    small = small.next;

                }

            } else {

                if (large == null) {

                    large = head;

                    largeHead = large;

                } else {

                    large.next = head;

                    large = large.next;

                }

            }

            head = next;

        }

        if(small == null) 

        {

            return largeHead;

        }

        small.next = largeHead;

        return smallHead;

    }



    public static void main(String args[]) {

        List list = new List(0);

        appendToTail(list, 9);

        appendToTail(list, 8);

        appendToTail(list, 7);

        appendToTail(list, 6);

        appendToTail(list, 5);

        appendToTail(list, 4);

        appendToTail(list, 3);

        appendToTail(list, 2);

        appendToTail(list, 1);

        print(list);

        print(partition(list, 5));

    }

}



class List {

    int data;

    List next;



    public List(int d) {

        this.data = d;

        this.next = null;

    }



    public List() {

    }

}