public class LowCommonNode {private class BinaryNode{BinaryNode left;BinaryNode right;int ele;public BinaryNode(int ele) {this.ele = ele;left = right = null;}}private BinaryNode root;private void buildTree(int[] arr){for (int i : arr) {insert(i);}}private void insert(int ele){root = insert(root, ele);}private BinaryNode insert(BinaryNode root, int ele){if(root == null)return new BinaryNode(ele);if(root.ele > ele)//insert leftroot.left = insert(root.left, ele);else if(root.ele < ele)root.right = insert(root.right, ele);elseroot.left = insert(root.left, ele);//相等时,放在左边return root;}/*** 求解二叉查找树中  node1 和 node2 代表的节点的 最低公共祖先结点* 首先让node1总是代表权值较小的那个结点.* 对于二叉查找树而言:* 如果根的权值处于 node1 和 node2 之间,则根就是它们的最低公共祖先结点* 如果根的权值比 node1 和 node2 都大,则它们的最低公共祖先结点在根的左子树中* 如果根的权值比 node1 和 node2 都小,则它们的最低公共祖先结点在根的右子树中*/public int lowestCommonParentNode(BinaryNode root, int node1, int node2){if(node1 > node2){int tmp = node1;node1 = node2;node2 = tmp;}assert node1 < node2;if(root == null)throw new IllegalArgumentException(" neither node1 nor node2 contains in binary search tree ");if(root.ele > node1 && root.ele < node2)return root.ele;if(root.ele > node1 && root.ele > node2)//if(root.ele > node2)//在左子树中查找最低公共祖先结点return lowestCommonParentNode(root.left, node1, node2);else//root.ele < node1//在右子树中查找最低公共祖先结点return lowestCommonParentNode(root.right, node1, node2);}//hapjin testpublic static void main(String[] args) {LowCommonNode lcn = new LowCommonNode();int[] arr = {20,10,30,5,15,25,40,12,18};lcn.buildTree(arr);//build a binary search tree// node1 and node2 should exist in arr,or will throw IllegalArgumentExceptionint node1 = 5;int node2 = 12;//should build Tree before invoke lowestCommonParentNode
        System.out.println(lcn.lowestCommonParentNode(lcn.root, node1, node2));}
}