在二叉树中找到两个节点的最近公共祖先

import java.util.*;//在二叉树中找到两个节点的最近公共祖先public class GetLowestTree{//二叉树节点的定义public static class Node{public int value;public Node left;public Node right;public Node(int data){this.value=data;}}//找到两个节点的最近公共祖先public static Node GetLowestAncestor(Node head,Node n1,Node n2){   //递归的出口if(head==null||n1==head||n2==head){return head;}         //递归调用Node left=GetLowestAncestor(head.left,n1,n2);  //左子树Node right=GetLowestAncestor(head.right,n1,n2); //右子树if(left!=null&&right!=null){return head;}return left!=null?left:right;}//***************************************************   // 直观打印二叉树public static void printTree(Node head) {System.out.println("Binary Tree:");printInOrder(head, 0, "H", 17);System.out.println();}public static void printInOrder(Node head, int height, String to, int len) {if (head == null) {return;}printInOrder(head.right, height + 1, "v", len);String val = to + head.value + to;int lenM = val.length();int lenL = (len - lenM) / 2;int lenR = len - lenM - lenL;val = getSpace(lenL) + val + getSpace(lenR);System.out.println(getSpace(height * len) + val);printInOrder(head.left, height + 1, "^", len);}public static String getSpace(int num) {String space = " ";StringBuffer buf = new StringBuffer("");for (int i = 0; i < num; i++) {buf.append(space);}return buf.toString();}//***************************************************  // 进阶问题--方法一(构造hash表)public static class Record1 {private HashMap<Node, Node> map;public Record1(Node head) {map = new HashMap<Node, Node>();if (head != null) {map.put(head, null);}setMap(head);}private void setMap(Node head) {if (head == null) {return;}if (head.left != null) {map.put(head.left, head);}if (head.right != null) {map.put(head.right, head);}setMap(head.left);setMap(head.right);}public Node query(Node o1, Node o2) {HashSet<Node> path = new HashSet<Node>();while (map.containsKey(o1)) {path.add(o1);o1 = map.get(o1);}while (!path.contains(o2)) {o2 = map.get(o2);}return o2;}}// 进阶问题--方法二public static class Record2 {private HashMap<Node, HashMap<Node, Node>> map;public Record2(Node head) {map = new HashMap<Node, HashMap<Node, Node>>();initMap(head);setMap(head);}private void initMap(Node head) {if (head == null) {return;}map.put(head, new HashMap<Node, Node>());initMap(head.left);initMap(head.right);}private void setMap(Node head) {if (head == null) {return;}headRecord(head.left, head);headRecord(head.right, head);subRecord(head);setMap(head.left);setMap(head.right);}private void headRecord(Node n, Node h) {if (n == null) {return;}map.get(n).put(h, h);headRecord(n.left, h);headRecord(n.right, h);}private void subRecord(Node head) {if (head == null) {return;}preLeft(head.left, head.right, head);subRecord(head.left);subRecord(head.right);}private void preLeft(Node l, Node r, Node h) {if (l == null) {return;}preRight(l, r, h);preLeft(l.left, r, h);preLeft(l.right, r, h);}private void preRight(Node l, Node r, Node h) {if (r == null) {return;}map.get(l).put(r, h);preRight(l, r.left, h);preRight(l, r.right, h);}public Node query(Node o1, Node o2) {if (o1 == o2) {return o1;}if (map.containsKey(o1)) {return map.get(o1).get(o2);}if (map.containsKey(o2)) {return map.get(o2).get(o1);}return null;}}public static void main(String[]args){//System.out.println("Hello");Node head=new Node(1);head.left=new Node(2);head.right=new Node(3);head.left.left=new Node(4);head.left.right=new Node(5);head.right.left=new Node(6);head.right.right=new Node(7);head.right.right.left=new Node(8);            printTree(head);        Node node=GetLowestAncestor(head,head.left,head.right);System.out.println(node.value);        Node o1 = head.left.right;Node o2 = head.right.left;// 生成map后方便多次查询--进阶问题Record1 record1 = new Record1(head);Record2 record2 = new Record2(head);System.out.println("o1 : " + o1.value);System.out.println("o2 : " + o2.value);System.out.println("ancestor : " + record1.query(o1, o2).value);System.out.println("ancestor : " + record2.query(o1, o2).value);o1 = head.left.left;o2 = head.left;System.out.println("o1 : " + o1.value);System.out.println("o2 : " + o2.value);System.out.println("ancestor : " + record1.query(o1, o2).value);System.out.println("ancestor : " + record2.query(o1, o2).value);o1 = head.right.left;o2 = head.right.right.left;System.out.println("o1 : " + o1.value);System.out.println("o2 : " + o2.value);System.out.println("ancestor : " + record1.query(o1, o2).value);System.out.println("ancestor : " + record2.query(o1, o2).value);}}