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```/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode() : val(0), left(nullptr), right(nullptr) {}
*     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
*     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
string ans;
void rootToStart(TreeNode* root, int startValue,int cnt) {
if(root == NULL)return;
if(root->val == startValue) {
for(int i=0;i<cnt;i++) {
ans.push_back('U');
}
return;
}

rootToStart( root->left, startValue, cnt+1);
rootToStart( root->right, startValue, cnt+1);

}

bool rootToDest(TreeNode* root, int destValue) {
if(root == NULL)return false;
if(root->val == destValue) {
return true;
}

ans.push_back('L');
if(rootToDest(root->left, destValue)) return true;

ans.pop_back();

ans.push_back('R');
if(rootToDest(root->right, destValue)) return true;
ans.pop_back();

return false;

}

TreeNode* findLCA(TreeNode* root, int startValue, int destValue) {
if(root == NULL)return NULL;

if(root->val == startValue || root->val == destValue) return root;

TreeNode* leftLCA = findLCA(root->left, startValue, destValue);
TreeNode* rightLCA = findLCA(root->right, startValue, destValue);

if(leftLCA == NULL) return rightLCA;
if(rightLCA == NULL) return leftLCA;

return root;
}

string getDirections(TreeNode* root, int startValue, int destValue) {
TreeNode* lca = findLCA(root, startValue, destValue);
rootToStart(lca, startValue, 0);
rootToDest(lca, destValue);
return ans;
}
};```