<p>You are given the <code>root</code> of a <strong>binary tree</strong> with <code>n</code> nodes. Each node is uniquely assigned a value from <code>1</code> to <code>n</code>. You are also given an integer <code>startValue</code> representing the value of the start node <code>s</code>, and a different integer <code>destValue</code> representing the value of the destination node <code>t</code>.</p>

<p>Find the <strong>shortest path</strong> starting from node <code>s</code> and ending at node <code>t</code>. Generate step-by-step directions of such path as a string consisting of only the <strong>uppercase</strong> letters <code>&#39;L&#39;</code>, <code>&#39;R&#39;</code>, and <code>&#39;U&#39;</code>. Each letter indicates a specific direction:</p>

<ul>
	<li><code>&#39;L&#39;</code> means to go from a node to its <strong>left child</strong> node.</li>
	<li><code>&#39;R&#39;</code> means to go from a node to its <strong>right child</strong> node.</li>
	<li><code>&#39;U&#39;</code> means to go from a node to its <strong>parent</strong> node.</li>
</ul>

<p>Return <em>the step-by-step directions of the <strong>shortest path</strong> from node </em><code>s</code><em> to node</em> <code>t</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/11/15/eg1.png" style="width: 214px; height: 163px;" />
<pre>
<strong>Input:</strong> root = [5,1,2,3,null,6,4], startValue = 3, destValue = 6
<strong>Output:</strong> &quot;UURL&quot;
<strong>Explanation:</strong> The shortest path is: 3 &rarr; 1 &rarr; 5 &rarr; 2 &rarr; 6.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/11/15/eg2.png" style="width: 74px; height: 102px;" />
<pre>
<strong>Input:</strong> root = [2,1], startValue = 2, destValue = 1
<strong>Output:</strong> &quot;L&quot;
<strong>Explanation:</strong> The shortest path is: 2 &rarr; 1.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the tree is <code>n</code>.</li>
	<li><code>2 &lt;= n &lt;= 10<sup>5</sup></code></li>
	<li><code>1 &lt;= Node.val &lt;= n</code></li>
	<li>All the values in the tree are <strong>unique</strong>.</li>
	<li><code>1 &lt;= startValue, destValue &lt;= n</code></li>
	<li><code>startValue != destValue</code></li>
</ul>

/**
 * 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 getDirections(TreeNode* root, int startValue, int destValue) {
        unordered_map <TreeNode* , TreeNode* > parent;
        queue <TreeNode*> q;
        q.push(root);
        TreeNode* start;
        TreeNode* dest;
        while(q.size()!=0){
            TreeNode* temp=q.front();
            q.pop();
            if(temp->val==startValue){
                start=temp;
            }
            if(temp->val==destValue){
                dest=temp;
            }
            if(temp->left!=NULL){
                q.push(temp->left);
                parent[temp->left]=temp;
            }
            if(temp->right!=NULL){
                q.push(temp->right);
                parent[temp->right]=temp;
            }
        }
        // cout<<start->val<<" "<<dest->val<<endl;
        unordered_set <TreeNode*> visited;
        unordered_map <TreeNode*, pair<TreeNode*, char>> path; 
        q.push(start);
        while(q.size()!=0){
            TreeNode* temp=q.front();
            q.pop();
            cout<<temp->val<<endl;
            if(temp==dest){
                break;
            }
            if(parent.find(temp)!=parent.end() && visited.find(parent[temp])==visited.end()){
                q.push(parent[temp]);
                visited.insert(parent[temp]);
                path[parent[temp]]={temp,'U'};
            }
            if(temp->left!=NULL && visited.find(temp->left)==visited.end()){
                q.push(temp->left);
                visited.insert(temp->left);
                path[temp->left]={temp,'L'};
            }
            if(temp->right!=NULL && visited.find(temp->right)==visited.end()){
                q.push(temp->right);
                visited.insert(temp->right);
                path[temp->right]={temp,'R'};
            }
        }
        string answer;
        TreeNode* temp=dest;
        // cout<<path[dest].second;
        while(temp!=start){
            answer.push_back(path[temp].second);
            temp=path[temp].first;
        }
        reverse(answer.begin(), answer.end());
        return answer;
    }
};
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