Leetcode 235 Lowest Common Ancestor of a Binary Search Tree

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Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.

According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself).”

        _______6______       /              \    ___2__          ___8__   /      \        /      \   0      _4       7       9         /  \         3   5

For example, the lowest common ancestor (LCA) of nodes 2 and 8 is 6. Another example is LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.

public class Solution235 {    public boolean findPath(TreeNode root, TreeNode p, List<TreeNode> result) {        if(root == null) return false;        if(root == p) {            result.add(root);            return true;        }        if(root.val >= p.val) {            result.add(root.left);            root = root.left;        } else {            result.add(root.right);            root = root.right;        }        findPath(root,p,result);        return true;    }    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {        List<TreeNode> listp = new ArrayList<TreeNode>();        List<TreeNode> listq = new ArrayList<TreeNode>();        listp.add(root);        listq.add(root);        findPath(root, p, listp);        findPath(root, q, listq);        TreeNode ans = root;        for (int i = 1, j = 1; i < listp.size() && j < listq.size(); i++, j++) {            if(listp.get(i).equals(listq.get(j))) {                ans = listp.get(i);            } else {                break;            }        }        return ans;    }    public static void main(String[] args) {        TreeNode p = null, q = null;        TreeNode root = new TreeNode(6);        root.left = new TreeNode(2);        p = root.left;        root.right = new TreeNode(8);        //q = root.right;        root.left.left = new TreeNode(0);        root.left.right = new TreeNode(4);        q = root.left.right;        root.left.right.left = new TreeNode(3);        root.left.right.right = new TreeNode(5);        root.right.left = new TreeNode(7);        root.right.right = new TreeNode(9);        TreeNode ans = new Solution235().lowestCommonAncestor(root, p, q);        System.out.println(ans.val);    }}

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