奇偶链表&按值分割链表(携程笔试)-java实现_链表奇偶拆分 java

一、将单链表的奇数节点和偶数节点分别排在一起，奇数偶数指的是节点编号;保持奇数节点和偶数节点的相对顺序；

输入：1->2->3->4->5->null
输出：1->3->5->2->4->null

思路：
* 1.创建两个链表，奇数链表和偶数链表；
* 2.遍历原链表，将奇数节点赋值给奇数链表，偶数节点赋值给偶数链表；
* 3.将偶数节点跟在奇数节点后面；

public ListNode oddEvenList(ListNode head) {
		if (head == null) {
			return null;
		}else if (head.next == null) {
			return head;
		}
		ListNode odd = new ListNode(0);
		ListNode oddCur = odd;
		ListNode even = new ListNode(0);
		ListNode evenCur = even;
		
		while (head != null) {
			int i = 0;
			if (i % 2 != 0) {
				oddCur.next = new ListNode(head.val);
				oddCur = oddCur.next;
			}else {
				evenCur.next = new ListNode(head.val);
				evenCur = evenCur.next;
			}
			head = head.next;
		}
		oddCur.next = even.next;
		return odd.next;
	}
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二、给定一个链表和一个整数k，将链表分成两部分，比k小的放在左边，比k大的放在右边；并且左右两部分各自的相对顺序不变。

* 输入:k=5, head:1->9->7->3->6->5->2
* 输出:1->3->5->2->9->7->6

public class OddEvenList {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		ListNode head = null;
		ListNode node = null;
		int k = scanner.nextInt();
		int i = 7;
//		while (scanner.hasNextInt()) {
		while (i-- != 0) {
			int val = scanner.nextInt();
			if (head == null) {
				node = new ListNode(val);
				head = node;
			}else {
				node.next = new ListNode(val);
				node = node.next;
			}
		}// end while
		head = partition(head, k);
		if (head != null) {
			System.out.print(head.val);
			head = head.next;
			while (head != null) {
				System.out.print(",");
				System.out.print(head.val);
				head = head.next;
			}
		}
		System.out.println();
	}
	public ListNode oddEvenList(ListNode head) {
		if (head == null) {
			return null;
		}else if (head.next == null) {
			return head;
		}
		ListNode odd = new ListNode(0);
		ListNode oddCur = odd;
		ListNode even = new ListNode(0);
		ListNode evenCur = even;
		
		while (head != null) {
			int i = 0;
			if (i % 2 != 0) {
				oddCur.next = new ListNode(head.val);
				oddCur = oddCur.next;
			}else {
				evenCur.next = new ListNode(head.val);
				evenCur = evenCur.next;
			}
			head = head.next;
		}
		oddCur.next = even.next;
		return odd.next;
	}
	/**
	 * 给定一个链表和一个整数k，将链表分成两部分，比k小的放在左边，比k大的放在右边；并且左右两部分各自的相对顺序不变。
	 * @param head
	 * @param k
	 * @return
	 */
	/**
	 * 输入:k=5, head:1->9->7->3->6->5->2
	 * 输出:1->3->5->2->9->7->6
	 */	
	public static ListNode partition(ListNode head, int k) {
		if (head == null || head.next == null) {
			return head;
		}
		ListNode small = new ListNode(0);
		ListNode smallCur = small;
		ListNode large = new ListNode(0);
		ListNode largeCur = large;
		
		while (head != null) {
			if (head.val <= k) {
				smallCur.next = new ListNode(head.val);
				smallCur = smallCur.next;
			}else {
				largeCur.next = new ListNode(head.val);
				largeCur = largeCur.next;
			}
			head = head.next;
		}
		smallCur.next = large.next;
		return small.next;
	}
}
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