2096. Step-By-Step Directions From a Binary Tree Node to Another

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    private List<String> paths = new ArrayList<>();
    public String getDirections(TreeNode root, int startValue, int destValue) {
        TreeNode LCA = getLCA(root, startValue, destValue);
        
        StringBuilder LCAtoStart = new StringBuilder();
        StringBuilder LCAtoDest = new StringBuilder();
        find(LCA, startValue, LCAtoStart);
        find(LCA, destValue, LCAtoDest);
        
        StringBuilder direction = new StringBuilder();
        for (char c : paths.get(0).toCharArray()) {
            direction.append("U");
        }
        for (char c : paths.get(1).toCharArray()) {
            direction.append(c);
        }
        return direction.toString();
    }
    
    private void find(TreeNode root, int value, StringBuilder sb) {
        if (root == null) {
            return;
        }
        if (root.val == value) {
            paths.add(sb.toString());
            return;
        }
        if (root.left != null) {
            find(root.left, value, sb.append("L"));
        }
        if (root.right != null) {
            find(root.right, value, sb.append("R"));
        }
        sb.deleteCharAt(sb.length() - 1);
        return;
    }
    
    private TreeNode getLCA(TreeNode root, int startValue, int destValue) {
        if (root == null) {
            return null;
        }
        if (root.val == startValue || root.val == destValue) {
            return root;
        }
        TreeNode left = getLCA(root.left, startValue, destValue);
        TreeNode right = getLCA(root.right, startValue, destValue);
        if (left != null && right != null) {
            return root; 
        } else {
            return left == null ? right : left;
        }
    } 
}