leetcode86. Partition List

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本文介绍了一种链表分区算法的实现方法，该算法能够确保所有小于给定值 x 的节点出现在大于等于 x 的节点之前，同时保持原有节点相对顺序不变。通过具体的 Java 代码示例展示了如何创建链表、进行分区操作及输出结果。

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Given a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x.

You should preserve the original relative order of the nodes in each of the two partitions.

For example,
Given 1->4->3->2->5->2 and x = 3,
return 1->2->2->4->3->5.

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package leetcode86;

public class Solution {
	public ListNode partition(ListNode head, int x) {
		if(head==null){
			return head;
		}
		ListNode newHead = new ListNode(-1);
		ListNode newHead2 = new ListNode(-1);
		ListNode r = newHead,r2=newHead2;
		ListNode p = head,q;
		while(p!=null){
			q=p.next;
			if(p.val<x){
				r.next=p;
				r=p;
				p=q;
				if(p!=null) q = q.next;
			}else{
				r2.next=p;
				r2=p;
				p=q;
				if(p!=null) q=q.next;
			}
		}
		r2.next=null;
		r.next=newHead2.next;
		return newHead.next;
	}
	public ListNode create(int[] a){
		ListNode head = new ListNode(a[0]);
		ListNode q = head;
		for(int i=1;i<a.length;i++){
			ListNode p = new ListNode(a[i]);
			p.next=null;
			q.next=p;
			q=p;
		}
		return head;
	}
	public void show(ListNode head){
		ListNode p = head;
		while(p!=null){
			System.out.println(p.val);
			p=p.next;
		}
	}
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int[] a = {1,4,3,2,5,2};
		Solution s = new Solution();
		ListNode head = s.create(a);
		s.show(head);
		System.out.println("*****************");
		head = s.partition(head, 3);
		s.show(head);
	}

}

class ListNode {
	int val;
	ListNode next;

	ListNode(int x) {
		val = x;
	}
}