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() {
    }
}