algorithm-class/体系学习班/class09/Code01_LinkedListMid.java

package class09;

import java.util.ArrayList;

public class Code01_LinkedListMid {

	public static class Node {
		public int value;
		public Node next;

		public Node(int v) {
			value = v;
		}
	}

	// head 头
	public static Node midOrUpMidNode(Node head) {
		if (head == null || head.next == null || head.next.next == null) {
			return head;
		}
		// 链表有3个点或以上
		Node slow = head.next;
		Node fast = head.next.next;
		while (fast.next != null && fast.next.next != null) {
			slow = slow.next;
			fast = fast.next.next;
		}
		return slow;
	}

	public static Node midOrDownMidNode(Node head) {
		if (head == null || head.next == null) {
			return head;
		}
		Node slow = head.next;
		Node fast = head.next;
		while (fast.next != null && fast.next.next != null) {
			slow = slow.next;
			fast = fast.next.next;
		}
		return slow;
	}

	public static Node midOrUpMidPreNode(Node head) {
		if (head == null || head.next == null || head.next.next == null) {
			return null;
		}
		Node slow = head;
		Node fast = head.next.next;
		while (fast.next != null && fast.next.next != null) {
			slow = slow.next;
			fast = fast.next.next;
		}
		return slow;
	}

	public static Node midOrDownMidPreNode(Node head) {
		if (head == null || head.next == null) {
			return null;
		}
		if (head.next.next == null) {
			return head;
		}
		Node slow = head;
		Node fast = head.next;
		while (fast.next != null && fast.next.next != null) {
			slow = slow.next;
			fast = fast.next.next;
		}
		return slow;
	}

	public static Node right1(Node head) {
		if (head == null) {
			return null;
		}
		Node cur = head;
		ArrayList<Node> arr = new ArrayList<>();
		while (cur != null) {
			arr.add(cur);
			cur = cur.next;
		}
		return arr.get((arr.size() - 1) / 2);
	}

	public static Node right2(Node head) {
		if (head == null) {
			return null;
		}
		Node cur = head;
		ArrayList<Node> arr = new ArrayList<>();
		while (cur != null) {
			arr.add(cur);
			cur = cur.next;
		}
		return arr.get(arr.size() / 2);
	}

	public static Node right3(Node head) {
		if (head == null || head.next == null || head.next.next == null) {
			return null;
		}
		Node cur = head;
		ArrayList<Node> arr = new ArrayList<>();
		while (cur != null) {
			arr.add(cur);
			cur = cur.next;
		}
		return arr.get((arr.size() - 3) / 2);
	}

	public static Node right4(Node head) {
		if (head == null || head.next == null) {
			return null;
		}
		Node cur = head;
		ArrayList<Node> arr = new ArrayList<>();
		while (cur != null) {
			arr.add(cur);
			cur = cur.next;
		}
		return arr.get((arr.size() - 2) / 2);
	}

	public static void main(String[] args) {
		Node test = null;
		test = new Node(0);
		test.next = new Node(1);
		test.next.next = new Node(2);
		test.next.next.next = new Node(3);
		test.next.next.next.next = new Node(4);
		test.next.next.next.next.next = new Node(5);
		test.next.next.next.next.next.next = new Node(6);
		test.next.next.next.next.next.next.next = new Node(7);
		test.next.next.next.next.next.next.next.next = new Node(8);

		Node ans1 = null;
		Node ans2 = null;

		ans1 = midOrUpMidNode(test);
		ans2 = right1(test);
		System.out.println(ans1 != null ? ans1.value : "无");
		System.out.println(ans2 != null ? ans2.value : "无");

		ans1 = midOrDownMidNode(test);
		ans2 = right2(test);
		System.out.println(ans1 != null ? ans1.value : "无");
		System.out.println(ans2 != null ? ans2.value : "无");

		ans1 = midOrUpMidPreNode(test);
		ans2 = right3(test);
		System.out.println(ans1 != null ? ans1.value : "无");
		System.out.println(ans2 != null ? ans2.value : "无");

		ans1 = midOrDownMidPreNode(test);
		ans2 = right4(test);
		System.out.println(ans1 != null ? ans1.value : "无");
		System.out.println(ans2 != null ? ans2.value : "无");

	}

}